SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

[Rule 13d-101]

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO § 240.13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO

§ 240.13d-1(a)

(Amendment No. 4)*

SPRINT CORPORATION

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

85207 U 10 5

(CUSIP Number)

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

August 5, 2013

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box:  ¨

NOTE: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (the “Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

(Continued on following pages)

EXPLANATORY NOTE

This Amendment No. 4 (this “Schedule 13D”) is being jointly filed on behalf of SoftBank Corp., a Japanese kabushiki kaisha (“SoftBank”), Starburst I, Inc., a Delaware corporation and wholly owned subsidiary of SoftBank (“Starburst I”) and Galaxy Investment Holdings, Inc., a Delaware corporation and wholly owned subsidiary of SoftBank (“Galaxy”, and together with SoftBank and Starburst I, the “Reporting Persons”, and each a “Reporting Person”) with respect to Sprint Corporation, a Delaware corporation (referred to herein as “New Sprint” or the “Issuer”). This Schedule 13D amends the Schedule 13D filed by SoftBank, Starburst I, New Sprint and Starburst III, Inc., a Kansas corporation (“Merger Sub”) on October 25, 2012, as amended on April 22, 2013 and June 11, 2013, and as amended and restated on July 12, 2013 (as amended and restated, the “Original 13D”), which relates to the common stock of New Sprint, par value $0.01 per share (the “New Sprint Common Stock”).

In connection with the completion of the Merger, as defined in the Agreement and Plan of Merger, dated October 15, 2012, by and among Sprint Nextel Corporation (“Sprint Nextel”), SoftBank, Starburst I, New Sprint, and Merger Sub, as amended on November 29, 2012, April 12, 2013 and June 10, 2013 (as amended, the “Merger Agreement”, a copy of which is attached hereto as Exhibits 99.2 through 99.5 and incorporated into Items 2 through 6 of this Schedule 13D by reference), Merger Sub was merged into Sprint Nextel, New Sprint became the parent company of Sprint Nextel, with Sprint Nextel becoming its wholly owned subsidiary, and Sprint Nextel changed its name to “Sprint Communications, Inc.” In connection with the Merger and by operation of Rule 12g-3(a) promulgated under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), New Sprint is the successor issuer to Sprint Nextel and has succeeded to the attributes of Sprint Nextel, including Sprint Nextel’s Securities and Exchange Commission (the “Commission”) file number (001-04721). The New Sprint Common Stock is deemed to be registered under Section 12(b) of the Exchange Act, and New Sprint is subject to the informational requirements of the Exchange Act, and the rules and regulations promulgated thereunder, and files reports and other information with the Commission using the Commission file number previously used by Sprint Nextel.

This Schedule 13D is being filed to reflect purchases of New Sprint Common Stock by Galaxy pursuant to a Rule 10b-18 Purchase Agreement (the “Purchase Agreement”) entered into by and between Galaxy and J.P. Morgan Securities LLC (“JPMS”) on August 1, 2013. Pursuant to the Purchase Agreement, Galaxy, through JPMS, intends to acquire approximately 2% of the outstanding shares of New Sprint Common Stock in compliance with Rule 10b-18 of the Securities Exchange Act (such purchases, the “Rule 10b-18 Purchases”). The Rule 10b-18 Purchases are intended to increase SoftBank’s beneficial ownership in New Sprint to approximately 80% of the outstanding shares of New Sprint Common Stock (not including the shares of New Sprint Common Stock underlying the Warrant, as defined below).

The Purchase Agreement is subject to immediate termination by either party upon verbal or written notice to the other party. The Purchase Agreement, a copy of which is attached hereto as Exhibit 99.8, is incorporated into this Schedule 13D by reference. Other than as set forth below, all Items in the Original 13D are unchanged. Capitalized terms used herein which are not defined herein have the meanings given to them in the Original 13D.

Item 2. Identity and Background.

Item 2 of the Original 13D is hereby amended and restated in its entirety to read as follows:

“(a) and (f) This Schedule 13D is being jointly filed on behalf of SoftBank, Starburst I and Galaxy.

The New Sprint Common Stock reported on this Schedule 13D is owned directly by Starburst I and Galaxy, as described in Item 5 to this Schedule 13D. SoftBank is included as a Reporting Person solely because it is the sole owner of both Starburst I and Galaxy. Pursuant to (i) SoftBank’s ownership of Starburst I and Galaxy, (ii) the Merger Agreement, (iii) the issuance by New Sprint to Starburst I of the New Sprint Warrant, dated July 10, 2013 (the “Warrant”, a copy of which is attached hereto as Exhibit 99.6 and incorporated into Items 2 through 6 of this Schedule 13D by reference), (iv) the Rule 10b-18 Purchases by Galaxy and (v) Rule 13d-5(b)(1) under the Exchange Act, SoftBank, Starburst I and Galaxy may be deemed to be a “group” and such “group” may be deemed to have acquired beneficial ownership for purposes of Section 13(d) of the Exchange Act, of all of the New Sprint Common Stock beneficially owned by such “group.” Starburst I expressly disclaims beneficial ownership with respect to the shares of New Sprint Common Stock deemed to be beneficially owned by SoftBank and Galaxy, except to the extent of Starburst I’s direct pecuniary interest in the shares of New Sprint Common Stock directly beneficially owned by Starburst I. Galaxy expressly disclaims beneficial ownership with respect to the shares of New Sprint Common Stock deemed to be beneficially owned by SoftBank and Starburst I, except to the extent of Galaxy’s direct pecuniary interest in the shares of New Sprint Common Stock directly beneficially owned by Galaxy.

Item 3. Source and Amount of Funds or Other Consideration.

Item 3 of the Original 13D is hereby amended and restated in its entirety to read as follows:

“The Reporting Persons own (directly or by being deemed a beneficial owner) the New Sprint Common Stock pursuant to (i) a reclassification exempt under Rule 16b-7 under the Exchange Act, in which New Sprint Class B Common Stock, par value $0.01 per share (the “New Sprint Class B Common Stock”), held by Starburst I was reclassified into 3,076,525,523 shares of New Sprint Common Stock, (ii) the issuance by New Sprint to Starburst I of the Warrant, which is subject to anti-dilution adjustment, as described in the Warrant and (iii) the Rule 10b-18 Purchases made by Galaxy.

SoftBank financed the acquisition of New Sprint Class B Common Stock by Starburst I through a combination of borrowings under a bridge loan agreement dated December 18, 2012 with Mizuho Corporate Bank, Ltd. (now Mizuho Bank, Ltd.), Sumitomo Mitsui Banking Corporation, The Bank of Tokyo-Mitsubishi UFJ, Ltd. and Deutsche Bank AG, Tokyo Branch; proceeds from a global offering of senior U.S. dollar and euro notes on April 23, 2013; and proceeds from Japanese domestic offerings of yen-denominated unsecured corporate bonds on March 1, 2013, March 12, 2013 and June 20, 2013.

Pursuant to the Merger Agreement, no additional consideration was payable in connection with the issuance to Starburst I of the Warrant to purchase 54,579,924 shares of New Sprint Common Stock at a price of $5.25 per share. The Warrant is exercisable at any time until July 10, 2018.

Between August 1, 2013 and August 5, 3013, Galaxy purchased 28,808,212 shares of New Sprint Common Stock pursuant to the Purchase Agreement, for an aggregate purchase price of $187,599,575.52, exclusive of any fees, commissions or other expenses. Galaxy’s Rule 10b-18 Purchases were financed from SoftBank’s general working capital.”

Item 4. Purpose of Transaction.

Purpose of the Transaction

Item 4 of the Original 13D is hereby amended and restated in its entirety to read as follows:

“Purpose of the Transaction

SoftBank may be deemed a beneficial owner of the New Sprint Common Stock in connection with the Merger and the subsequent reclassification described in Item 3 to this Schedule 13D, the issuance of the Warrant, and, through Galaxy, the shares of New Sprint Common Stock acquired through the Rule 10b-18 Purchases. The Merger is intended to make Sprint a stronger, more competitive company that will deliver significant benefits to U.S. consumers based on SoftBank’s expertise in the deployment of next-generation wireless networks and track record of success in taking share in mature markets from larger telecommunications competitors.

Starburst I directly owns the New Sprint Common Stock in connection with the Merger and the subsequent reclassification described in Item 3 to this Schedule 13D, and may be deemed to beneficially own the shares of New Sprint Common Stock issuable upon exercise of the Warrant.

On August 1, 2013, Galaxy commenced making Rule 10b-18 Purchases pursuant to the Purchase Agreement. As of August 5, 2013, Galaxy had directly acquired 28,808,212 shares of New Sprint Common Stock, or approximately 0.73% of the outstanding shares of New Sprint Common Stock.

Plans or Proposals

The Reporting Persons, as stockholders in New Sprint, intend to review their investment in New Sprint and have discussions with representatives of New Sprint and/or other stockholders of New Sprint from time to time and, as a result thereof, may at any time and from time to time determine to take any available course of action and may take any steps to implement any such course of action. Such review, discussions, actions or steps may involve one or more of the types of transactions specified in clauses (a) through (j) of Item 4 of this Schedule 13D, including purchase or sale of New Sprint Common Stock, business combination or other extraordinary corporate transactions, sales or purchases of material assets, changes in the board of directors or management of New Sprint, changes to New Sprint’s business or corporate structure, shared service agreements, collaborations, joint ventures and other business arrangements between or involving SoftBank and New Sprint. Any action or actions the Reporting Persons might undertake in respect of the New Sprint Common Stock will be dependent upon the Reporting Persons’ review of numerous factors, including, among other things, the price level and liquidity of the New Sprint Common Stock; general market and economic conditions; ongoing evaluation of New Sprint’s business, financial condition, operations, prospects and strategic alternatives; the relative attractiveness of alternative business and investment opportunities; tax considerations; and other factors and future developments. Notwithstanding anything to the contrary herein, the Reporting Persons specifically reserve the right to change their intentions with respect to any or all of such matters.”

Item 5. Interest in Securities of the Issuer.

Item 5(a), (b) and (c) of the Original 13D are hereby amended and restated in their entirety to read as follows:

“(a)-(b) As of August 5, 2013, each Reporting Person may be deemed to have beneficial ownership (within the meaning of Rule 13d-3 under the Exchange Act) and shared power to vote or direct the vote of up to the number of shares of New Sprint Common Stock set forth in the table below and may be deemed to constitute a “group” under Section 13(d) of the Act as described in Item 2 of this Schedule 13D, which is incorporated herein by reference.

(c) The information contained in Items 3 and 4 to this Schedule 13D is herein incorporated by reference. In connection with closing of the Merger, all Sprint Nextel common stock and options to acquire Sprint Nextel common stock held by directors and executive officers of Sprint Nextel (immediately prior to the consummation of the Merger) were exchanged for Merger Consideration (as defined in the Merger Agreement) or options to purchase New Sprint Common Stock pursuant to the terms of the Merger Agreement.

The weighted average price per share for the Rule 10b-18 Purchases made on August 1, 2013, exclusive of any fees, commissions or other expenses, was $6.28, and such shares were purchased in multiple transactions at prices ranging from $6.05 to $6.45, exclusive of any fees, commissions or other expenses. The weighted average price per share for the Rule 10b-18 Purchases made on August 2, 2013, exclusive of any fees, commissions or other expenses, was $6.62, and such shares were purchased in multiple transactions at prices ranging from $6.41 to $6.75, exclusive of any fees, commissions or other expenses. The weighted average price per share for the Rule 10b-18 Purchases made on August 5, 2013, exclusive of any fees, commissions or other expenses, was $6.76, and such shares were purchased in multiple transactions at prices ranging from $6.53 to $6.88, exclusive of any fees, commissions or other expenses. The Reporting Persons undertake to provide New Sprint, any stockholder of New Sprint, or the Staff of the Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this Item 5(c) to this Schedule 13D.

Except as set forth above or incorporated herein, none of (i) the Reporting Persons and, (ii) to the Reporting Persons knowledge, the persons set forth on Appendix A-1, A-2 or A-3 of this Schedule 13D has effected any transaction in New Sprint Common Stock during the past 60 days.”

Item 7. Material to be Filed as Exhibits.

Item 7 of the Original 13D is hereby amended and supplemented as follows:

By replacing Exhibit 99.1 with the following:

By adding the following as Exhibits 99.8, 99.9, 99.10 and 99.11:

SIGNATURES

After reasonable inquiry and to the best of our knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete and correct.

Dated: August 5, 2013

Appendix A-3

EXECUTIVE OFFICERS AND DIRECTORS

OF

GALAXY INVESTMENT HOLDINGS, INC.

Set forth below is a list of each executive officer and director of Galaxy Investment Holdings, Inc. setting forth the business address and present principal occupation or employment (and the name and address of any corporation or organization in which such employment is conducted) of each person.

EXHIBIT INDEX

Exhibit 99.1

JOINT FILING AGREEMENT

JOINT FILING AGREEMENT (this “Agreement”), dated as of August 5, 2013, by and among SoftBank Corp., a Japanese kabushiki kaisha (“SoftBank”), Starburst I, Inc., a Delaware corporation (“Starburst I”), and Galaxy Holdings, Inc., a Delaware corporation (“Galaxy”, and collectively with SoftBank and Starburst I, the “Reporting Persons”, and each a “Reporting Person”).

WHEREAS, pursuant to (i) SoftBank’s ownership of Starburst I and Galaxy, (ii) a reclassification exempt under Rule 16b-7 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), in which Starburst II, Inc. Class B Common Stock, par value $0.01 per share, held by Starburst I was reclassified into 3,076,525,523 shares of Sprint Corporation (formerly known as Starburst II, Inc. and referred to herein as “New Sprint”) common stock, par value $0.01 per share (the “New Sprint Common Stock”), (iii) the issuance by New Sprint to Starburst I of the New Sprint Warrant, dated July 10, 2013 (the “Warrant”), which is subject to anti-dilution adjustment, as described in the Warrant, (iv) purchases of New Sprint Common Stock made in compliance with Rule 10b-18 (“Rule 10b-18”) under the Exchange Act by Galaxy, and (v) Rule 13d-5(b)(1) under the Exchange Act, SoftBank, Starburst I and Galaxy may be deemed to be a “group” and such “group” may be deemed to have acquired beneficial ownership, for purposes of Section 13(d) of the Exchange Act, of all of the New Sprint Common Stock beneficially owned by such “group”; and

WHEREAS, each of the Reporting Persons desires by this Agreement to provide for the joint filing of a Statement on Schedule 13D or any amendments thereto (as amended from time to time, the “Joint Schedule 13D”) with respect to the Reporting Persons’ respective beneficial ownership of New Sprint Common Stock.

NOW, THEREFORE, the Reporting Persons hereby agree as follows:

1. Joint Filing. Pursuant to Rule 13d-1(k) of the Exchange Act, each of the Reporting Persons shall cooperate to jointly prepare and file the Joint Schedule 13D with respect to their respective beneficial ownership of shares of New Sprint Common Stock on behalf of the Reporting Persons and all necessary or appropriate amendments thereto. The Reporting Persons agree that this Agreement may be included as an exhibit to the Joint Schedule 13D and any amendments thereto, and any amendments to the Joint Schedule 13D may be filed without the necessity of filing additional joint filing agreements. For purposes of this Agreement, the terms “beneficial ownership” and “beneficial owner” shall have the meanings given to them pursuant to Rule 13d-3 of the Exchange Act.

2. Amendments. Each Reporting Person agrees that if (a) it or any of its Affiliates (as such term is defined in the Agreement and Plan of Merger, dated as of October 15, 2012, as amended, by and between Sprint Nextel Corporation, SoftBank, Starburst I, New Sprint and Starburst III, Inc.), takes any action that would require the Reporting Persons to amend the Joint Schedule 13D or (b) any information concerning such Reporting Person or any of its Affiliates set forth in the Joint Schedule 13D is or becomes inaccurate in any material respect, such Reporting Person shall notify the other Reporting Persons no later than one business day thereafter, and shall cause an appropriate amendment to the Joint Schedule 13D to be promptly prepared and distributed to the other Reporting Persons for review.

3. Reasonable Opportunity to Review. Each Reporting Person agrees to provide the other Reporting Persons a reasonable opportunity to review and comment on each proposed amendment to the Joint Schedule 13D.

4. Information; Responsibility.

(a) Each Reporting Person represents and warrants to the other Reporting Persons that the information concerning such Reporting Person and any of its Affiliates contained in the Joint Schedule 13D is, or any amendment thereto will be, true, correct and complete in all material respects and in accordance with all applicable laws.

(b) In accordance with Rule 13d-1(k) of the Exchange Act, each Reporting Person shall be responsible for the completeness and accuracy of the information concerning such Reporting Person contained therein, but shall not be responsible for the completeness and accuracy of the information concerning any other Reporting Person contained therein, unless such Reporting Person knows or has reason to believe that such information is inaccurate.

5. Indemnification. Each Reporting Person agrees to indemnify each other Reporting Person for any losses, claims, liabilities or expenses (including reasonable legal fees and expenses) resulting from, or arising in connection with, the breach by such Reporting Person of any representations, warranties or agreements in this Agreement.

6. Termination; Survival. Any Reporting Person may terminate its obligation to continue to jointly file future amendments to the Joint Schedule 13D by delivering written notice to each other Reporting Person at least two business days prior to the effective date of such termination in which case the provisions of this Agreement solely with respect to such Reporting Person shall terminate; provided, that (x) paragraphs 5, 6, 7, 8 and 9 hereof shall survive such termination and (y) such Reporting Person shall continue to be subject to its indemnification obligations under this Agreement for any breach by such Reporting Person hereunder existing at the time of such termination. In addition, following the termination by any Reporting Person pursuant to this Section 6 and thereafter for so long as such Reporting Person or any of its Affiliates may be deemed to beneficially own any of the New Sprint Common Stock held by any of the other Reporting Persons or any of their Affiliates, or for so long as any other Reporting Person or any of their Affiliates

may be deemed to beneficially own any of the New Sprint Common Stock held by such Reporting Person or any of its Affiliates, such Reporting Person shall promptly (and in any event within one business day after the filing) notify each other Reporting Person in writing of the filing of any Schedule 13D or amendment thereof with respect to its or any of its Affiliates’ beneficial ownership of New Sprint Common Stock.

7. Governing Law; Jurisdiction; Waiver of Jury Trial. This Agreement will be governed in all respects by the laws of the State of Delaware. No suit, action or proceeding with respect to this Agreement may be brought in any court or before any similar authority other than in a court of competent jurisdiction in the State of Delaware, and the parties to this Agreement submit to the exclusive jurisdiction of those courts for the purpose of a suit, proceeding or judgment. Each party to this Agreement irrevocably waives any right it may have had to bring an action in any other court, domestic or foreign, or before any similar domestic or foreign authority. Each of the parties to this Agreement irrevocably and unconditionally waives trial by jury in any legal action or proceeding (including any counterclaim) in relation to this Agreement.

8. Counterparts; Facsimile Signatures. This Agreement may be executed in any number of counterparts, each of which will be an original, but all of which together will constitute one instrument. This Agreement may be executed by facsimile or electronically-sent signature(s).

9. Notices. All notices and other communications required or permitted under this Agreement will be in writing and shall be sent by facsimile (including a written confirmation of transmission), in the case of SoftBank and Starburst I to their facsimile numbers set forth in the Merger Agreement, and in the case of Galaxy to +1 617 928 9302. All notices given as provided under this Agreement shall be deemed to have been effectively given on the date the facsimile transmission is sent if sent during normal business hours of the recipient or, if not, on the next business day.

[Remainder of page intentionally left blank]

IN WITNESS WHEREOF, the undersigned have executed this Agreement as of the date first above written.

Exhibit 99.8

10b-18 PURCHASE AGREEMENT

(NON-EXCLUSIVE)

August 1, 2013

Galaxy Investment Holdings, Inc.

1209 Orange Street

Wilmington, DE 19801

This letter agreement (this “Letter Agreement”) confirms the terms and conditions under which J.P. Morgan Securities LLC (“JPMS”) will act as non-exclusive agent for Galaxy Investment Holdings, Inc. (the “Purchaser”) in connection with the Purchaser’s program (the “Program”) to purchase shares of common stock, par value $0.01 (the “Securities”), of Sprint Corporation (the “Issuer”).

(a) Unless otherwise agreed to, the Purchaser will provide JPMS with instructions on a daily basis in respect of the Program regarding the total number of Securities JPMS is authorized to purchase and target amounts of Securities to be acquired during the day succeeding such instruction and the maximum price or the range of prices to be paid therefore. Except as otherwise provided in this Letter Agreement, JPMS shall determine, in its sole discretion, the timing, amount, prices and manner of purchase of Securities on any day, so long as such purchases are consistent with the instruction provided by the Purchaser for such day. JPMS agrees that no person who exercises influence, directly or indirectly, on its behalf in effecting purchases of Securities pursuant to the Program may do so while aware of material, non-public information relating to the Securities or the Issuer.

(b) In the event that JPMS, in its discretion, determines that it is appropriate with regard to any legal, regulatory or self-regulatory requirements or related internal policies and procedures (whether or not such requirements, policies or procedures are imposed by law or have been voluntarily adopted by JPMS) for JPMS to refrain from purchasing Securities or to purchase fewer than the number of Securities otherwise specified in the instructions provided by the Purchaser on any day, then JPMS may, in its sole discretion, elect that the number of Securities purchased shall be reduced for such day to an amount determined by JPMS in its discretion.

(a) This Letter Agreement and the transactions contemplated herein have been duly authorized by the Purchaser and have been reviewed, to the extent required, pursuant to or under any and all applicable policies and procedures of the Issuer applicable to purchases of Securities by its “affiliated purchasers”; this Letter Agreement is the valid and binding agreement of the Purchaser, enforceable in accordance with its terms; performance of the transactions contemplated herein will not violate any law, rule, regulation, order, judgment or decree applicable to the Purchaser or conflict with or result in a breach of or constitute a

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default under any agreement or instrument to which the Purchaser is a party or by which it or any of its property is bound or its certificate of incorporation or by-laws; and no governmental, administrative or official consent, approval or authorization is required for performance of the transactions contemplated herein.

(b) At any time during the term of this Letter Agreement that JPMS has been instructed to purchase Securities in connection with the Program, the Purchaser is not aware of any material nonpublic information regarding the Issuer or the Securities. In the event that the Purchaser affirmatively instructs JPMS not to purchase Securities on any day or for any period, the Purchaser agrees that it shall not communicate to JPMS the reason for such instruction.

(c) The Purchaser is not entering into this Letter Agreement to create actual or apparent trading activity in the Securities (or any security convertible into or exchangeable for the Securities) or to raise or depress the price of the Securities (or any security convertible into or exchangeable for the Securities) for the purpose of inducing others to buy or sell Securities, and will not engage in any other securities or derivative transaction to such ends.

(d) The Purchaser acknowledges that JPMS is a “financial institution” and “financial participant” within the meaning of Sections 101(22) and 101(22A), respectively, of Title 11 of the United States Code (the “Bankruptcy Code”). The parties hereto further agree and acknowledge that each transaction under this Letter Agreement is intended to be a “securities contract” as defined in Section 741(7) of the Bankruptcy Code and each payment or delivery of cash, Securities or other property or assets hereunder is a “settlement payment” within the meaning of Section 741(8) of the Bankruptcy Code, and the parties hereto are to be entitled to the protections afforded by, among other Sections, Sections 362(b)(6), 362(b)(27), 362(o), 546(e), 546(j), 555 and 561 of the Bankruptcy Code.

(e) Prior to 8:00 a.m., New York City time on each day on which JPMS is instructed to purchase Securities pursuant to this Letter Agreement, the Purchaser will provide to JPMS, in addition to the instructions described in Section 5(a), all information, other than publicly reported trading volumes, as it may be reasonably requested by JPMS that is necessary for JPMS to calculate the maximum number of Securities that may be purchased on such day in accordance with the volume condition set forth in Rule 10b-18 including without limitation any block purchases by or on behalf of the Purchaser, the Issuer or any other affiliated purchaser of the Purchaser, the Issuer, and JPMS shall be entitled to rely on such information so provided.

(f) Without limiting the generality of Section 3 of this Letter Agreement, the Purchaser shall notify JPMS in writing at least five business days prior to engaging in any transaction that would cause the Securities (or any securities convertible into, exchangeable for or linked in value to the Securities) to be subject to a “restricted period” under, and as defined in, Regulation M under the Exchange Act.

J.P. Morgan Securities LLC

383 Madison Avenue, 5^th Floor

New York, NY 10179

Attention: James F. Smith

Email: james.f.smith@jpmorgan.com

Telephone: (212) 622-2922 Fax: (917) 464-8885

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or at such other address as may from time to time be designated by notice to the Purchaser in writing; and

SoftBank Capital

38 Glen Avenue

Newtown Center, MA 02459

or at such other address as may from time to time be designated by notice to JPMS in writing.

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If the foregoing correctly sets forth our agreement, please sign the form of acceptance below.

Exhibit 99.9

POWER OF ATTORNEY

Know all by these presents that the undersigned hereby constitutes and appoints each of Kazuhiko Kasai, Yoshimitsu Goto, Masato Suzaki, Ronald D. Fisher and Joshua O. Lubov signing singly, the undersigned’s true and lawful attorney-in-fact to:

The undersigned hereby grants to each such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact’s substitute or substitutes, shall lawfully do or cause to be done by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorneys-in-fact, in serving in such capacity at the request of the undersigned, are not assuming any of the undersigned’s responsibilities in respect of SoftBank’s responsibility to comply with Sections 13 and 16 of the Securities Exchange Act of 1934, as amended. This Power of Attorney shall remain in full force and effect until SoftBank is no longer required to file Forms 3, 4, or 5 or Schedule 13D and 13G and any Amendments thereto with respect to SoftBank’s holdings of and transactions in securities issued by the Company, unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorneys-in-fact. This Power of Attorney supersedes and revokes, as of the date hereof, all powers providing authority similar to the above-referenced authority granted in this Power of Attorney.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of this 5th day of August, 2013.

Exhibit 99.10

POWER OF ATTORNEY

Know all by these presents that the undersigned hereby constitutes and appoints each of Masayoshi Son, Kazuhiko Kasai, Yoshimitsu Goto, Masato Suzaki and Joshua O. Lubov signing singly, the undersigned’s true and lawful attorney-in-fact to:

The undersigned hereby grants to each such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact’s substitute or substitutes, shall lawfully do or cause to be done by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorneys-in-fact, in serving in such capacity at the request of the undersigned, are not assuming any of the undersigned’s responsibilities in respect of Starburst I’s responsibility to comply with Sections 13 and 16 of the Securities Exchange Act of 1934, as amended. This Power of Attorney shall remain in full force and effect until Starburst I is no longer required to file Forms 3, 4, or 5 or Schedule 13D and 13G and any Amendments thereto with respect to Starburst I’s holdings of and transactions in securities issued by the Company, unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorneys-in-fact. This Power of Attorney supersedes and revokes, as of the date hereof, all powers providing authority similar to the above-referenced authority granted in this Power of Attorney.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of this 5^th day of August, 2013.

Exhibit 99.11

POWER OF ATTORNEY

Know all by these presents that the undersigned hereby constitutes and appoints each of Masayoshi Son, Kazuhiko Kasai, Yoshimitsu Goto, Masato Suzaki and Joshua O. Lubov signing singly, the undersigned’s true and lawful attorney-in-fact to:

The undersigned hereby grants to each such attorney-in-fact full power and authority to do and perform any and every act and thing whatsoever requisite, necessary, or proper to be done in the exercise of any of the rights and powers herein granted, as fully to all intents and purposes as the undersigned might or could do if personally present, with full power of substitution or revocation, hereby ratifying and confirming all that such attorney-in-fact, or such attorney-in-fact’s substitute or substitutes, shall lawfully do or cause to be done by virtue of this Power of Attorney and the rights and powers herein granted. The undersigned acknowledges that the foregoing attorneys-in-fact, in serving in such capacity at the request of the undersigned, are not assuming any of the undersigned’s responsibilities in respect of Galaxy’s responsibility to comply with Sections 13 and 16 of the Securities Exchange Act of 1934, as amended. This Power of Attorney shall remain in full force and effect until Galaxy is no longer required to file Forms 3, 4, or 5 or Schedule 13D and 13G and any Amendments thereto with respect to Galaxy’s holdings of and transactions in securities issued by the Company, unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorneys-in-fact. This Power of Attorney supersedes and revokes, as of the date hereof, all powers providing authority similar to the above-referenced authority granted in this Power of Attorney.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be executed as of this 5th day of August, 2013.