SC 13G

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

XO Holdings Inc.

(Name of Issuer)

Common Stock, par value $0.01 per share
(Title of Class of Securities)

98417K106
(CUSIP Number)

December 31, 2008
(Date of Event Which Requires Filing of this Statement)

     Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

o Rule 13d-1(b)
þ Rule 13d-1(c)
o Rule 13d-1(d)

     *The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

     The information required in the remainder of this cover page shall not be deemed to be “filed” for purpose of Section 18 of the Securities Exchange Act of 1934 (“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).

Page 1 of 9 Pages

CUSIP No. 98417K106  13G Page 2  of  9   Pages

1	NAMES OF REPORTING PERSONS Diamondback Master Fund, Ltd.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a)   þ
	(b)   o
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION
	Cayman Islands, British West Indies
		5	SOLE VOTING POWER
NUMBER OF			0
SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			9,636,600 shares of Common Stock
EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0
WITH		8	SHARED DISPOSITIVE POWER
			9,636,600 shares of Common Stock
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	9,636,600 shares of Common Stock
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
	5.29%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	CO

CUSIP No. 98417K106  13G Page 3  of  9   Pages

1	NAMES OF REPORTING PERSONS Diamondback Capital Management, LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a)   þ
	(b)   o
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION
	State of Delaware
		5	SOLE VOTING POWER
NUMBER OF			0
SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			9,636,600 shares of Common Stock
EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0
WITH		8	SHARED DISPOSITIVE POWER
			9,636,600 shares of Common Stock
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	9,636,600 shares of Common Stock
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
	5.29%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	OO

CUSIP No. 98417K106  13G Page 4  of  9   Pages

1	NAMES OF REPORTING PERSONS DBCM Partners, LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a)   þ
	(b)   o
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION
	State of Delaware
		5	SOLE VOTING POWER
NUMBER OF			0
SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			9,636,600 shares of Common Stock
EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0
WITH		8	SHARED DISPOSITIVE POWER
			9,636,600 shares of Common Stock
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
	9,636,600 shares of Common Stock
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)
	o
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
	5.29%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	OO

CUSIP No. 98417K106  13G Page 5  of  9   Pages

TABLE OF CONTENTS

	Item 1
	Item 2(a). Name of Person Filing
	Item 2(b). Address of Principal Business Office
	Item 2(c). Citizenship
	Item 2(d) Title of Class of Securities
	Item 2(e) CUSIP Number
	Item 3. If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a
	Item 4. Ownership
	Item 5. Ownership of Five Percent or Less of a Class
	Item 6. Ownership of More than Five Percent on Behalf of Another Person
	Item 7. Identification and Classification of the Subsidiary Which Acquired
	Item 8. Identification and Classification of Members of the Group
	Item 9. Notice of Dissolution of Group
	Item 10. Certification
SIGNATURES
EX-99.I: JOINT FILING AGREEMENT

Item 1.

(a) Name of Issuer

XO Holdings Inc. (the “Company”)

(b) Address of Issuer’s Principal Executive Offices

13865 Sunrise Valley Drive
Herndon, Virginia 20171

Item 2(a). Name of Person Filing

Item 2(b). Address of Principal Business Office

Item 2(c). Citizenship

Diamondback Master Fund, Ltd.
c/o Morgan Stanley Fund Services (Bermuda) Ltd.
Clarendon House, 2 Church Street
Hamilton HM DX, Bermuda
Citizenship: Cayman Islands, British West Indies

Diamondback Capital Management, LLC
One Landmark Square, 15th Floor
Stamford, CT 06901
Citizenship: State of Delaware

DBCM Partners, LLC
One Landmark Square, 15th Floor
Stamford, CT 06901
Citizenship: State of Delaware

Item 2(d) Title of Class of Securities

Common Stock, $0.01 par value (“Common Stock”)

Item 2(e) CUSIP Number

98417K106

Item 3. If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:

(a)	[ ]	Broker or dealer registered under Section 15 of the Act (15 U.S.C. 78o).
(b)	[ ]	Bank as defined in Section 3(a)(6) of the Act (15 U.S.C. 78c).
(c)	[ ]	Insurance company as defined in Section 3(a)(19) of the Act (15 U.S.C. 78c).
(d)	[ ]	Investment company registered under Section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8).
(e)	[ ]	An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);

CUSIP No. 98417K106  13G Page 6  of  9   Pages

(f)	[ ]	An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F);
(g)	[ ]	A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G);
(h)	[ ]	A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	[ ]	A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	[ ]	Group, in accordance with Rule 13d-1(b)(1)(ii)(J).

If this statement is filed pursuant to Rule 13d-1(c), check this box. [X]

Item 4. Ownership

     Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a) Amount beneficially owned:

     As of the date of this filing, (i) Diamondback Master Fund, Ltd. beneficially owns 9,636,600 shares of Common Stock and (ii) each of Diamondback Capital Management, LLC and DBCM Partners, LLC may be deemed the beneficial owner of the 9,636,600 shares of Common Stock beneficially owned by Diamondback Master Fund, Ltd.

     Diamondback Capital Management, LLC is the investment manager of Diamondback Master Fund, Ltd. DBCM Partners, LLC is the managing member of Diamondback Capital Management, LLC. Each of Chad Loweth, Richard Sapanski and Richard H. Schimel (the “Diamondback Principals”) serve as managing members of DBCM Partners, LLC. The foregoing should not be construed in and of itself as an admission by any Reporting Person or the Diamondback Principals as to beneficial ownership of the shares of Common Stock owned by another Reporting Person. In addition, each of Diamondback Capital Management, LLC, DBCM Partners, LLC and the Diamondback Principals disclaims beneficial ownership of the shares of Common Stock owned by Diamondback Master Fund, Ltd.

(b) Percent of class:

     The Company’s Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2008 filed on November 10, 2008, indicates that the total number of outstanding shares of Common Stock as of November 5, 2008 was 182,075,035. Based on the Company’s outstanding shares of Common Stock as of November 5, 2008, each of Diamondback Master Fund, Ltd., Diamondback Capital Management, LLC and DBCM Partners, LLC may be deemed to beneficially own 5.29% of the outstanding shares of Common Stock of the Company. The foregoing should not be construed in and of itself as an admission by any Reporting Person as to beneficial ownership of shares of Common Stock owned by another Reporting Person.

(c) Number of shares as to which such person has:

(i)	Sole power to vote or to direct the vote
	0

CUSIP No. 98417K106  13G Page 7  of  9   Pages

(ii)	Shared power to vote or to direct the vote
	See Item 4(a)
(iii)	Sole power to dispose or to direct the disposition of
	0
(iv)	Shared power to dispose or to direct the disposition of
	See Item 4(a)

Item 5. Ownership of Five Percent or Less of a Class

     Not applicable.

Item 6. Ownership of More than Five Percent on Behalf of Another Person

     Not applicable.

Item 7. Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or
Control Person

     Not applicable.

Item 8. Identification and Classification of Members of the Group

     See Exhibit I.

Item 9. Notice of Dissolution of Group

     Not applicable.

Item 10. Certification

     By signing below each of the undersigned certifies that, to the best of its knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

Exhibits:

Exhibit I: Joint Filing Agreement, dated as of January 7, 2009, by and among Diamondback Master Fund, Ltd., Diamondback Capital Management, LLC and DBCM Partners, LLC

CUSIP No. 98417K106  13G Page 8  of  9   Pages

SIGNATURES

     After reasonable inquiry and to the best of its knowledge and belief, each of the undersigned certifies that the information with respect to it set forth in this statement is true, complete, and correct.

Dated: January 7, 2009
DIAMONDBACK MASTER FUND, LTD.		DIAMONDBACK CAPITAL MANAGEMENT, LLC
By:	/s/ Chad Loweth	By:	/s/ Mark Hadlock
Name:	Chad Loweth	Name:	Mark Hadlock
Title:	Chief Operating Officer	Title:	Chief Compliance Officer
DBCM PARTNERS, LLC
By:	/s/ Chad Loweth
Name:	Chad Loweth
Title:	Managing Member

EX-99.I

CUSIP No. 98417K106  13G Page 9  of  9   Pages

EXHIBIT I

JOINT FILING AGREEMENT

This will confirm the agreement by and among the undersigned that the Schedule 13G filed with the Securities and Exchange Commission on or about the date hereof with respect to the beneficial ownership by the undersigned of the common stock, $0.01 par value, of XO Holdings Inc., is being filed, and all amendments thereto will be filed, on behalf of each of the persons and entities named below in accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended. This Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument.

Dated as of January 07, 2009
DIAMONDBACK MASTER FUND, LTD.		DIAMONDBACK CAPITAL MANAGEMENT, LLC
By:	/s/ Chad Loweth	By:	/s/ Mark Hadlock
Name:	Chad Loweth	Name:	Mark Hadlock
Title:	Chief Operating Officer	Title:	Chief Compliance Officer
DBCM PARTNERS, LLC
By:	/s/ Chad Loweth
Name:	Chad Loweth
Title:	Managing Member