UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) December 17, 2012

SPRINT NEXTEL CORPORATION

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (800) 829-0965

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On December 17, 2012, Sprint Nextel Corporation (the “Company”) and Clearwire Corporation (“Clearwire”) issued a joint press release announcing the execution of an Agreement and Plan of Merger (the “Merger Agreement”), entered into as of December 17, 2012, by and among the Company, Collie Acquisition Corp. and Clearwire. Pursuant to the terms of the Merger Agreement, Collie Acquisition Corp. will merge with and into Clearwire, with Clearwire surviving the merger as a wholly owned subsidiary of the Company (the “Merger”). In connection with the execution of the Merger Agreement, the Company entered into a Note Purchase Agreement with Clearwire, Clearwire Communications, LLC and Clearwire Finance, Inc. pursuant to which the Company agreed to provide interim financing to Clearwire in an aggregate amount of up to $800 million through the purchase of exchangeable notes. In addition, Clearwire entered into a Voting and Support Agreement (the “Voting Agreement”) dated as of December 17, 2012, with certain of its other stockholders. Pursuant to the terms of the Voting Agreement, such stockholders have agreed, among other things, to vote shares of Clearwire owned by them in favor of approving and adopting the Merger Agreement. A copy of the press release is attached hereto as Exhibit 99.1 and incorporated by reference herein.

In addition, on December 17, 2012, the Company and Clearwire provided supplemental information regarding the Merger in connection with presentations to analysts and investors. A copy of the investor presentation is attached hereto as Exhibit 99.2 and incorporated by reference herein.

The information contained in this Current Report on Form 8-K is being furnished to comply with Regulation FD. Such information shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, and shall not be deemed to be incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, whether made before or after the date hereof and regardless of any general incorporation language in such filings, except as expressly set forth by specific reference in such a filing.

(d) Exhibits

The following exhibits are filed with this report:

Cautionary Statement Regarding Forward-Looking Statements

This Current Report on Form 8-K includes “forward-looking statements” within the meaning of the securities laws. The words “may,” “could,” “should,” “estimate,” “project,” “forecast,” intend,” “expect,” “anticipate,” “believe,” “target,” “plan,” “providing guidance” and similar expressions are intended to identify information that is not historical in nature.

This Current Report on Form 8-K contains forward-looking statements relating to the proposed Merger between the Company and Clearwire pursuant to the Merger Agreement and the related transactions (collectively, the “transaction”). All statements, other than historical facts, including statements regarding the expected timing of the closing of the transaction; the ability of the parties to complete the transaction considering the various closing conditions; the expected benefits and synergies of the transaction; the competitive ability and position of the Company and Clearwire; and any assumptions underlying any of the foregoing, are forward-looking statements. Such statements are based upon current plans, estimates and expectations that are subject to risks, uncertainties and assumptions. The inclusion of such statements should not be regarded as a representation that such plans, estimates or expectations will be achieved. You should not place undue reliance on such statements. Important factors that could cause actual results to differ materially from such plans, estimates or expectations include, among others, (i) any conditions imposed in connection with the transaction, (ii) approval of the transaction by Clearwire

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stockholders, (iii) the satisfaction of various other conditions to the closing of the transaction contemplated by the Merger Agreement, (iv) legal proceedings that may be initiated related to the transaction, and (v) other factors discussed in Clearwire’s and the Company’s Annual Reports on Form 10-K for their respective fiscal years ended December 31, 2011, their other respective filings with the U.S. Securities and Exchange Commission (the “SEC”) and the proxy statement and other materials that will be filed with the SEC by Clearwire in connection with the transaction. There can be no assurance that the transaction will be completed, or if it is completed, that it will close within the anticipated time period or that the expected benefits of the transaction will be realized.

None of the Company, Clearwire or Collie Acquisition Corp. undertakes any obligation to update any forward-looking statement to reflect events or circumstances after the date on which the statement is made or to reflect the occurrence of unanticipated events. Readers are cautioned not to place undue reliance on any of these forward-looking statements.

Additional Information and Where to Find It

In connection with the transaction, Clearwire will file a proxy statement and other materials with the SEC. INVESTORS AND SECURITY HOLDERS ARE ADVISED TO READ THE PROXY STATEMENT AND OTHER RELEVANT MATERIALS WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT CLEARWIRE AND THE TRANSACTION. Investors and security holders may obtain free copies of these documents (when they are available) and other documents filed with the SEC at the SEC’s web site at www.sec.gov. In addition, the documents filed by Clearwire with the SEC may be obtained free of charge by contacting Clearwire at Clearwire, Attn: Investor Relations, (425) 505-6178. Clearwire’s filings with the SEC are also available on its website at www.corporate.clearwire.com.

Participants in the Solicitation

Clearwire and its officers and directors and the Company and its officers and directors may be deemed to be participants in the solicitation of proxies from Clearwire stockholders with respect to the transaction. Information about Clearwire officers and directors and their ownership of Clearwire common shares is set forth in the proxy statement for Clearwire’s 2012 Annual Meeting of Stockholders, which was filed with the SEC on April 30, 2012. Information about the Company’s officers and directors is set forth in the Company’s Annual Report on Form 10-K for the year ended December 31, 2011, which was filed with the SEC on February 27, 2012. Investors and security holders may obtain more detailed information regarding the direct and indirect interests of the participants in the solicitation of proxies in connection with the transaction by reading the preliminary and definitive proxy statements regarding the transaction, which will be filed by Clearwire with the SEC.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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EXHIBIT INDEX

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