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-2(a)

(Amendment No. 4)*

Clearwire Corporation

(Name of Issuer)

Class A Common Stock

(Title of Class of Securities)

18538Q105

(CUSIP Number)

Pamela E. Powers

Executive Vice President, Secretary and Treasurer

Crest Financial Limited

JP Morgan Chase Tower

600 Travis, Suite 6800

Houston, TX 77002

Tel: (713) 222 6900

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

Copies to:

Stephen M. Gill

Kai Haakon E. Liekefett

Vinson & Elkins LLP

First City Tower

1001 Fannin Street, Suite 2500

Houston, TX 77002

Tel: (713) 758 2222

March 19, 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)

This Amendment No. 4 (this “Amendment”) amends and supplements the Statement on Schedule 13D (the “Schedule 13D”) of Crest Financial Limited (“CFL”), Crest Investment Company (“CIC”), the Jamal and Rania Daniel Revocable Trust (the “Jamal and Rania Daniel Trust”), Mr. Jamal Daniel, Mrs. Rania Daniel, DTN LNG, LLC (“DTN LNG”), DTN Investments, LLC (“DTN Investments”), the Daria Daniel 2003 Trust (the “Daria Daniel Trust”), the Thalia Daniel 2003 Trust (the “Thalia Daniel Trust”), the Naia Daniel 2003 Trust (the “Naia Daniel Trust”), Mr. John M. Howland, Mr. Eric E. Stoerr, the Halim Daniel 2012 Trust (the “Halim Daniel Trust”), Mr. Michael Wheaton, solely in his capacity as trustee of the Halim Daniel Trust, Mr. Halim Daniel, Uniteg Holding SA (“Uniteg”), Mila Hotels International SA (“Mila”) and Crest Switzerland, LLC (“Crest Switzerland” and, together with CFL, CIC, the Jamal and Rania Daniel Trust, Mr. Jamal Daniel, Mrs. Rania Daniel, DTN LNG, DTN Investments, the Daria Daniel Trust, the Thalia Daniel Trust, the Naia Daniel Trust, Mr. Howland, Mr. Stoerr, the Halim Daniel Trust, Mr. Wheaton, Mr. Halim Daniel, Uniteg, Mila and Crest Switzerland, the “Reporting Persons”) that was filed in respect of Clearwire Corporation (the “Issuer”) on June 1, 2012 and amended by Amendment No. 1 filed on November 7, 2012 (“Amendment No. 1”), Amendment No. 2 filed on December 18, 2012 (“Amendment No. 2”) and Amendment No. 3 filed on March 13, 2013 (“Amendment No. 3”).

Item 4 of the Schedule 13D is hereby amended and supplemented by adding the following paragraphs after the third paragraph thereof:

CFL recently engaged the proxy solicitation firm D.F. King & Co., Inc. (“DF King”) to assist CFL in its opposition against the proposed merger of the Issuer with Sprint Nextel Corporation (the “Sprint-Clearwire Merger”).

On March 19, 2013, CFL made a demand to obtain a stockholder list and certain related records of the Issuer pursuant to Section 220 of the Delaware General Corporation Law (the “Demand Letter”). CFL intends to use this information to communicate with other stockholders of the Issuer regarding the corporate affairs of the Issuer, including, without limitation, the solicitation of proxies regarding the proposed Sprint-Clearwire Merger. A copy of the Demand Letter is attached hereto as Exhibit 2 and is incorporated herein by reference. The description herein of the Demand Letter is qualified in its entirety by reference to the Demand Letter.

On March 20, 2013, CFL issued a press release (the “Press Release”). A copy of the Press Release is attached hereto as Exhibit 3. In the Press Release, CFL announces the engagement of DF King and the demand of the Issuer’s stockholder list.

CFL INTENDS TO FILE OTHER DOCUMENTS WITH THE U.S. SECURITIES AND EXCHANGE COMMISSION (THE “SEC”) REGARDING THE PROPOSED SPRINT-CLEARWIRE MERGER. BEFORE MAKING ANY VOTING OR INVESTMENT DECISION, INVESTORS AND SECURITY HOLDERS OF THE ISSUER ARE URGED TO READ SUCH OTHER DOCUMENTS REGARDING THE PROPOSED MERGER, CAREFULLY IN THEIR ENTIRETY, BECAUSE THEY CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER. INVESTORS AND SECURITY HOLDERS OF THE ISSUER MAY OBTAIN FREE COPIES OF OTHER DOCUMENTS FILED WITH, OR FURNISHED TO, THE SEC BY CFL AT THE SEC’S WEBSITE AT WWW.SEC.GOV.

Item 5 of the Schedule 13D is hereby amended by restating the first paragraph thereof as follows:

(a) The Reporting Persons may be deemed to be the beneficial owner of, in the aggregate, 57,653,419 Purchased Shares, representing approximately 8.2% of the outstanding Shares based upon the 699,157,146 Shares stated to be outstanding as of March 7, 2013 according to the Issuer’s Amendment No. 1 to the Preliminary Proxy Statement on Schedule 14A filed on March 12, 2013.

Item 6 of the Schedule 13D is hereby amended and restated in its entirety as follows:

Other than Asset Purchase Agreement as described in Item 3 hereof (which has been fully performed by the parties thereto in 2004), the Joint Filing Agreement attached hereto as Exhibit 1, the Demand Letter attached hereto as Exhibit 2, the Press Release attached hereto as Exhibit 3, the Press Release attached to Amendment No. 3 as Exhibit 2, the FCC Letter and the Report attached to Amendment No. 3 as Exhibit 3, the Press Release attached to Amendment No. 2 as Exhibit 2, the Stockholder Letter attached to Amendment No. 1 as Exhibit 2 and the Press Release attached to Amendment No. 1 as Exhibit 3, neither the Reporting Persons nor, to the best of the Reporting Persons’ knowledge, any person named on Schedule A hereto, has any contracts, arrangements, understandings or relationships (legal or otherwise) among the persons named in Item 2 and between such persons and any person with respect to any securities of the Issuer, including but not limited to, transfer or voting of any of the securities, finder’s fees, joint ventures, loan or option arrangements, puts or calls, guarantees of profits, division of profits or loss, or the giving or withholding of proxies.

The following documents are filed as exhibits:

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

Date: March 19, 2013

EXHIBIT INDEX

Exhibit 1

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, the persons named below agree to the joint filing on behalf of each of them of a statement on Schedule 13D (including amendments thereto) with respect to the Class A Common Stock of Clearwire Corporation and further agree that this Joint Filing Agreement be included as an Exhibit to such joint filings. In evidence thereof, the undersigned, being duly authorized, have executed this Joint Filing Agreement this 19^th day of March, 2013.

Exhibit 2

March 19, 2013

Clearwire Corporation

1475 120^th Avenue NE

Attention: Mr. Erik Prusch

President and Chief Executive Officer

Bellevue, WA 98005

Dear Mr. Prusch:

Crest Financial Limited, a Texas limited partnership (the “Requesting Stockholder”), is the beneficial owner of at least 100 shares of Class A common stock, par value $0.0001 per share, of Clearwire Corporation, a Delaware corporation (the “Company”). Attached hereto as Exhibit A is documentary evidence of the Requesting Stockholder’s beneficial ownership of at least 100 shares of Class A common stock of the Company as of March 19, 2013, and such documentary evidence is a true and correct copy of what it purports to be. The Requesting Stockholder continues to own the shares reflected on Exhibit A.

Pursuant to Section 220 of the Delaware General Corporation Law (the “DGCL”), the Requesting Stockholder hereby demands, during the Company’s usual hours for business, to inspect, and to make copies and extracts from, the Company’s stock ledger and list of stockholders, including the following information:

(a) A complete record or list of the holders of (i) shares of the Company’s capital stock (“Stock”) and (ii) warrants, rights and options entitling the holders thereof to purchase from the Company shares of Stock (“Rights”), in each case (i) and (ii) certified by the Company or its transfer agent and showing in respect of each such holder (A) the name, last known business, residence or mailing address, and telephone number of each such holder; (B) the number of shares of Stock and Rights held by each such holder; (C) the name of such holder on each certificate; (D) all existing certificate numbers for such holder; (E) the date each certificate was issued to each such holder; (F) the amount of each such holder’s shares of Stock or Rights represented by each certificate number; and (G) any indications that any such holder’s certificate is restricted in any way, including any transfer restrictions on such certificate.

(b) A complete record or list of the holders of Stock and Rights who are participants in any employee stock ownership, stock purchase, stock option, retirement, restricted stock, incentive, profit sharing, dividend reinvestment or any similar plan of the Company in which voting of shares under the plan is controlled, directly or indirectly, individually or collectively, by such plan’s participants, showing in respect of each such holder (i) the name, last known business, residence or mailing address, and telephone number of each such holder; (ii) the number of shares of Stock and Rights attributable to each such participant in any such plan; and (iii) the name, business address and telephone number of the trustee or administrator of any such plan, and a detailed explanation of the voting treatment not only of shares of Stock for which the

trustee or administrator receives instructions from participants, but also shares of Stock for which either they do not receive instructions or shares of Stock which are outstanding in any such plan but are unallocated to any participant.

(c) A complete record or list of the holders of Stock and Rights and respondent banks who have elected to receive electronic copies of proxy materials with respect to meetings of stockholders of the Company pursuant to Rule 14a-16(j)(2) of the Exchange Act.

(d) All transfer journals and daily transfer sheets showing changes in the names, addresses and number of shares of holders of Stock or Rights which are in or come into the possession of the Company or any of its transfer agents or registrars, or which can reasonably be obtained from brokers, dealers, banks, clearing agencies, voting trustees or their respective nominees.

(e) All information in or which comes into possession or control of the Company or any of its transfer agents or registrars, or which can reasonably be obtained from brokers, dealers, banks, clearing agencies, voting trustees or their respective nominee, concerning the names, addresses and number of shares of Stock and Rights held by the participating brokers and banks named in the individual nominee names of Cede & Co. or other similar depositories or nominees, including respondent bank lists.

(f) All information in or that comes into the Company’s possession, or that can reasonably be obtained from brokers, dealers, banks, clearing agencies, voting trustees or their respective nominee (including Broadridge Financial Services), relating to the names of the beneficial owners of Stock or Rights pursuant to Rule 14b-1(c) or Rule 14b-2(c) under the Securities Exchange Act of 1934, as amended, including a Non Objecting Beneficial Owners or “NOBO” list.

(g) All stop lists or stop transfer lists relating to any shares of Stock or Rights.

(h) In respect of all information referred to in paragraphs (a) through (g) above, (i) electronic media containing such information, (ii) the computer processing data necessary for the Requesting Stockholder to make use of such information on electronic media, and (iii) a hard copy printout of such information for verification purposes (all information referred to in paragraphs (a) through (h) above, collectively, the “Stocklist Materials”).

(i) A complete copy of the Company’s bylaws (the “Bylaws”).

The Requesting Stockholder demands that all Stocklist Materials and the Bylaws be made available to the Requesting Stockholder or its designees, as of the most recent date available, no later than the fifth business day after the date hereof. In addition, the Requesting Stockholder demands that (i) any updates, changes, modifications, corrections, additions or deletions to any of the Stocklist Materials (including, for the avoidance of doubt, daily DTC updates) be immediately furnished to the Requesting Stockholder as such updates, modifications, additions or deletions become available to the Company, its agents or other representatives; and (ii) all

2

Stocklist Materials be confirmed or updated and immediately furnished to the Requesting Stockholder as of the record date (the “Record Date”) in respect of the special meeting (the “Special Meeting”) of the stockholders of the Company to consider the Company’s proposals in respect of the Agreement and Plan of Merger, dated as of December 17, 2012, as amended from time to time, among Sprint Nextel Corporation, Collie Acquisition Corp., a wholly-owned subsidiary of Sprint, and the Company, as set forth in the proxy statement of the Company filed with the Securities and Exchange Commission on February 1, 2013, as amended on March 2, 2013 and from time to time thereafter. Lastly, the Requesting Stockholder demands that any and all changes whatsoever to the Bylaws made hereafter through the Special Meeting, including, without limitation, any amendment to the existing Bylaws, any adoption of any new Bylaws or deletions of any of the existing Bylaws, be immediately furnished to the Requesting Stockholder.

The purpose of this demand is to enable the Requesting Stockholder to communicate with fellow stockholders of the Company regarding the corporate affairs of the Company, including, without limitation, the solicitation of proxies regarding the Company’s proposals to be considered at the Special Meeting.

The Requesting Stockholder has designated to conduct the inspection of the Stocklist Materials requested herein: (i) Vinson & Elkins L.L.P. and its partners, associates, employees and other persons designated by Vinson & Elkins L.L.P.; and (ii) D.F. King & Co., Inc., its directors, officers, employees and other persons designated by D.F. King & Co., Inc. A copy of the power-of-attorney granted to such designees is attached hereto as Exhibit B. The Requesting Stockholder will pay the reasonable costs of obtaining the Stocklist Materials and the Bylaws and agrees to keep the Stocklist Materials confidential pursuant to the confidentiality agreement attached hereto as Exhibit C.

Pursuant to Section 220 of the DGCL, the Company is required to respond to this demand within five business days of the date hereof. Accordingly, please advise the Requesting Stockholder’s counsel at Vinson & Elkins L.L.P., Stephen M. Gill, Esq., at 713.758.4458 and Kai Haakon E. Liekefett, Esq., at 713.758.3839, as promptly as practicable within the requisite timeframe, when and where the Stocklist Materials will be made available to the Requesting Stockholder or its designees. If the Company contends that this demand is incomplete or is otherwise deficient in any respect, please notify the Requesting Stockholder immediately in writing, with a copy to (i) Stephen M. Gill, Esq., Vinson & Elkins L.L.P., 1001 Fannin Street, Suite 2500, Houston, Texas 77002-6706, telephone number 713.758.4458, facsimile number 713.615.5956, and email sgill@velaw.com; and (ii) Kai Haakon E. Liekefett, Esq., Vinson & Elkins L.L.P., 1001 Fannin Street, Suite 2500, Houston, Texas 77002-6706, telephone number 713.758.3839, facsimile number 713.615.5678, and email kliekefett@velaw.com, setting forth the facts or law that the Company contends support its position and specifying any additional information believed to be required. In the absence of such prompt notice, the Requesting Stockholder will assume that the Company agrees that this demand complies in all respects with the requirements of the DGCL.

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Exhibit 3

FOR IMMEDIATE RELEASE:

Contact: Jeffrey Birnbaum, (202) 661-6367, JBirnbaum@BGRPR.com

Crest Financial Limited Makes Demand for Clearwire’s Shareholders List and Hires Proxy Solicitation Firm D.F. King & Co.

HOUSTON, March 20, 2013 – Crest Financial Limited, a Texas-based investment company, announced today that it has hired proxy-solicitation firm D. F. King & Co., Inc. to help it oppose the proposed acquisition of Clearwire Corporation (NASDAQ: CLWR) by Sprint Nextel Corporation. As part of this effort, Crest has demanded that Clearwire make available the company’s list of shareholders. Crest is the largest Clearwire shareholder unaligned with Sprint, holding approximately 3.9% of all common stock of Clearwire.

The Sprint-Clearwire merger agreement requires the approval of holders of a majority of the Clearwire common stock not held by Sprint, which means that the transaction would not be approved if shareholders with approximately 25% of all common stock of Clearwire either vote against the merger or do not vote at all. Accordingly, in addition to the Clearwire shares held by Crest, only approximately 21.1% of the other shareholders need to vote against the Sprint-Clearwire merger or not vote at all in order to block the transaction.

Crest has filed a lawsuit in Delaware against Sprint and the directors of Clearwire because Crest believes that the defendants breached their fiduciary duties by scheming to extract value from Clearwire at the expense of the minority shareholders. Crest has also petitioned the Federal Communications Commission in Washington, D.C., to stop the proposed Softbank-Sprint and Sprint-Clearwire mergers because they would treat minority shareholders of Clearwire unfairly and the mergers would not be in the public’s best interest. A copy of Crest’s petition can be found here: www.bancroftpllc.com/crest.

“Crest Financial believes that Clearwire’s shareholders will reject Sprint’s unfair offer for Clearwire,” Dave Schumacher, Crest’s general counsel, said. “Our actions today are aimed at achieving this result. Crest is determined to do whatever it can to stop Sprint’s efforts to extract for itself the value of Clearwire’s trove of wireless spectrum and to harm minority shareholders and the public interest. We look forward to sharing with Clearwire’s minority shareholders more information on Sprint’s coercive merger offer.”

D. F. King & Co. is a leading full-service proxy solicitation and corporate communications firm. It specializes in proxy contests and tender offers.

Important Legal Information

Crest intends to file other documents with the U.S. Securities and Exchange Commission (the “SEC”) regarding the proposed acquisition of Clearwire, as contemplated by the Agreement and Plan of Merger dated as of December 17, 2012 among Clearwire, Sprint Nextel Corporation, a Kansas corporation (“Sprint”), and Collie Acquisition Corp., a Delaware corporation and wholly-owned subsidiary of Sprint. Before making any voting or investment decision, investors and security holders of Clearwire are urged to read such other documents regarding the proposed acquisition, carefully in their entirety, because they contain important information about the proposed transaction. Investors and security holders of Clearwire may obtain free copies of other documents filed with, or furnished to, the SEC by Crest at the SEC’s website at www.sec.gov.

Forward-looking Statements

Certain statements contained herein are forward-looking statements including, but not limited to, statements that are predications of or indicate future events, trends, plans or objectives. Undue reliance should not be placed on such statements because, by their nature, they are subject to known and unknown risks and uncertainties. Forward-looking statements are not guarantees of future activities and are subject to many risks and uncertainties. Due to such risks and uncertainties, actual events may differ materially from those reflected or contemplated in such forward-looking statements. Forward-looking statements can be identified by the use of the future tense or other forward-looking words such as “believe,” “expect,” “anticipate,” “intend,” “plan,” “should,” “may,” “will,” believes,” “continue,” “strategy,” “position” or the negative of those terms or other variations of them or by comparable terminology.