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. 19)*

Clearwire Corporation

(Name of Issuer)

Class A Common Stock

(Title of Class of Securities)

18538Q105

(CUSIP Number)

David K. Schumacher

General Counsel

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

May 30, 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. 19 (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”) and Crest Switzerland, LLC (“Crest Switzerland” and, together with CFL, CIC, the Jamal and Rania Daniel Trust, Mr. Jamal Daniel, Mrs. 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, solely in his capacity as trustee of the Halim Daniel Trust, Mr. Halim Daniel, Uniteg 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”), Amendment No. 3 filed on March 13, 2013 (“Amendment No. 3”), Amendment No. 4 filed on March 20, 2013 (“Amendment No. 4”), Amendment No. 5 filed on April 4, 2013 (“Amendment No. 5”), Amendment No. 6 filed on April 9, 2013 (“Amendment No. 6”), Amendment No. 7 filed on April 11, 2013 (“Amendment No. 7”), Amendment No. 8 filed on April 23, 2013 (“Amendment No. 8”), Amendment No. 9 (“Amendment No. 9”) filed on April 25, 2013, Amendment No. 10 filed on May 7, 2013 (“Amendment No. 10”), Amendment No. 11 filed on May 9, 2013 (“Amendment No. 11”), Amendment No. 12 filed on May 13, 2013 (“Amendment No. 12”), Amendment No. 13 filed on May 17, 2013 (“Amendment No. 13”), Amendment No. 14 filed on May 20, 2013 (“Amendment No. 14”), Amendment No. 15 filed on May 22, 2013 (“Amendment No. 15”), Amendment No. 16 filed on May 24, 2013 (“Amendment No. 16”), Amendment No. 17 filed on May 28, 2013 (“Amendment No. 17”) and Amendment No. 18 filed on May 29, 2013 (“Amendment No. 18”).

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

On May 30, 2013, CFL sent a letter to the board of directors of the Issuer (the “May 30 Letter to the Board”) and issued a press release relating thereto (the “May 30 Press Release”). In the May 30 Letter to the Board, CFL urged the board of directors of the Issuer to reverse its recommendation in favor of the merger of the Issuer with Sprint Nextel Corporation following DISH Network Corporation’s $4.40 per share tender offer announced on May 29, 2013. A copy of the May 30 Letter to the Board is attached hereto as Exhibit 2 and a copy of the May 30 Press Release is attached hereto as Exhibit 3, each of which are incorporated herein by reference. The descriptions herein of the May 30 Letter to the Board and the May 30 Press Release are qualified in their entirety by reference to the May 30 Letter to the Board and the May 30 Press Release.

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 May 30 Letter to the Board attached hereto as Exhibit 2, the May 30 Press Release attached hereto as Exhibit 3, the May 28 Press Release attached to Amendment No. 18 as Exhibit 2, the May 28 FCC Letter attached to Amendment No. 18 as Exhibit 3, the May 29 Press Release attached to Amendment No. 18 as Exhibit 4, the May 28 Letter to Stockholders attached to Amendment No. 17 as Exhibit 2, the May 28 Press Release attached to Amendment No. 17 as Exhibit 3, the May 23 Press Release attached to Amendment No. 16 as Exhibit 2, the May 21 Letter to Stockholders attached to Amendment No. 15 as Exhibit 2, the May 21 Letter to the Board attached to Amendment No. 15 as Exhibit 3, the May 21 Press Release attached to Amendment No. 15 as Exhibit 4, the May 20 Letter to Stockholders attached to Amendment No. 14 as Exhibit 2, the May 20 Letter to the Board attached to Amendment No. 14 as Exhibit 3; the May 20 Press Release attached to Amendment No. 14 as Exhibit 4, the May 17 Letter to Stockholders attached to Amendment No. 13 as Exhibit 2, the May 17 Press Release attached to Amendment No. 13 as Exhibit 3, the May 16 Letter to Stockholders attached to Amendment No. 13 as Exhibit 4, the May 16 Press Release attached to Amendment No. 13 as Exhibit 5, the Press Release attached to Amendment No. 12 as Exhibit 2, the Presentation to Stockholders attached to Amendment No. 11 as Exhibit 2, the Press Release attached to Amendment No. 11 as Exhibit 3, the Press Release attached to Amendment No. 10 as Exhibit 2, the Letter to Stockholders attached to Amendment No. 10 as Exhibit 3, the Power of Attorney for the Daria Daniel Trust attached to Amendment No. 10 as Exhibit 4, the Power of Attorney for the Thalia Daniel Trust attached to Amendment No. 10 as Exhibit 5, the Power of Attorney for the Naia Daniel Trust attached to Amendment No. 10 as Exhibit 6, the Power of Attorney for John M. Howland attached to Amendment No. 10 as Exhibit 7, the Press Release attached to Amendment No. 9 as Exhibit 2, the Power of Attorney for the Jamal and Rania Daniel Trust attached to Amendment No. 9 as Exhibit 3, the Power of Attorney for Jamal Daniel attached to Amendment No. 9 as Exhibit 4, the Power of Attorney for Rania Daniel attached to Amendment No. 9 as Exhibit 5, the Power of Attorney for Eric E. Stoerr attached to Amendment No. 9 as Exhibit 6, the Power of Attorney for the Halim Daniel Trust attached to Amendment No. 9 as Exhibit 7, the Power of Attorney for Halim Daniel attached to Amendment No. 9 as Exhibit 8, the Power of Attorney for Michael Wheaton attached to Amendment No. 9 as Exhibit 9, the Power of Attorney for Uniteg attached to Amendment No. 9 as Exhibit 10, the Board Letter attached to Amendment No. 8 as Exhibit 2, the April 23 Press Release attached to Amendment No. 8 as Exhibit 3, the April 22 Press Release attached to Amendment No. 8 as Exhibit 4, the FCC Letter attached to Amendment No. 8 as Exhibit 5, the Press Release attached to Amendment No. 7 as Exhibit 2, the Press Release attached to Amendment No. 6 as Exhibit 2, the FCC Letter attached to Amendment No. 6 as Exhibit 3, the Letter to the Board attached to Amendment No. 5 as Exhibit 2, the April 3 Press Release attached to Amendment No. 5 as Exhibit 3, the Demand Letter attached to Amendment No. 4 as Exhibit 2, the March 20 Press Release attached to Amendment No. 4 as Exhibit 3, the March 12 Press Release attached to Amendment No. 3 as Exhibit 2, the FCC Letter 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: May 30, 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 30th day of May, 2013.

Exhibit 2

CREST FINANCIAL LIMITED

JPMorgan Chase Tower

600 Travis, Suite 6800

Houston, Texas 77002

May 30, 2013

VIA FEDERAL EXPRESS AND FACSIMILE

John W. Stanton

Chairman, Board of Directors

Clearwire Corporation

1475 120th Avenue NE

Bellevue, WA 98005

Dear Mr. Stanton:

Crest Financial Limited (“Crest”) urges the Clearwire Board of Directors (the “Board”) to consider genuinely DISH Network Corporation’s (“DISH”) tender offer for all outstanding shares of Clearwire Corporation (“Clearwire” or the “Company”) for $4.40 per share. The Board has an obligation to consider DISH’s offer and, in light of the offer, to recommend that stockholders vote against Sprint Nextel Corporation’s (“Sprint”) offer at the special meeting scheduled for tomorrow. To ensure against further defaults and misjudgments, the Board should immediately reconstitute the Special Committee with newly appointed, truly independent directors and empower the Special Committee with the full authority of the Board to evaluate the DISH offer and any other offer for the Company that may be made after the Board conducts a fair and transparent process that encourages these offers, and to make decisions about interim financing.

Clearwire must break free of Sprint’s oppressive control and unlock the Company’s true value by going through with tomorrow’s shareholder meeting, and terminating the merger agreement with Sprint following the Clearwire stockholders’ rejection of the Sprint merger proposal. Once released from the ill-advised merger agreement with Sprint, you will be able to begin an open and competitive bidding process for the Company that will include DISH as well as any other competing bids. As Crest has been saying for some time, the battle for Clearwire and its valuable spectrum assets is just beginning. You, the Clearwire Board, are duty bound to ensure that this process gives full value of the Company and its assets to all stockholders—not just Sprint.

The Board has a fiduciary obligation to give full consideration to DISH’s offer, which is clearly actionable, and any other eventual offers that would trump the DISH offer. DISH’s offer for Clearwire confirms what Crest and others have been saying for months: Clearwire is the crown jewel, and the Company can realize its true value only through a competitive bidding process. DISH has initiated that process, and it is your legal obligation to pursue DISH’s offer and other potential offers now.

To that end, you are obligated to recommend against Sprint’s lower-priced offer. The Board must encourage Clearwire’s stockholders to reject Sprint’s latest bid at tomorrow’s special meeting. Perhaps the only favorable term in the otherwise oppressive merger agreement with

Sprint is the provision that you can change your recommendation and advise the stockholders to vote AGAINST the deal without paying a termination fee. You should exercise that option now. After the Clearwire stockholders accept your revised recommendation and vote AGAINST the Sprint offer, the Clearwire Board can terminate the unfair Sprint merger agreement, consider DISH’s offer, and solicit direct bids from others. Clearwire can pursue this course with the assurance that it will be able to continue operations during the competitive bidding process because Crest stands by its offer to provide the Company with $240.0 million in convertible financing, and is even willing to improve the exchange ratio to $2.50 per share (from the previous ratio of $2.00 per share) to match DISH’s proposed financing terms.

DISH’s proposal is superior to Sprint’s latest incremental bump and prior offers in every way. Most obviously, DISH has bid $1.00 more per share than Sprint’s “best and final offer.” This is a 29% premium over Sprint’s latest bid. Moreover, DISH’s tender offer is more favorable to minority stockholders than Sprint’s attempted squeeze-out. Though DISH’s offer is available to all stockholders, it does not force any minority stockholders to sell against their will. DISH’s offer would also reduce Sprint’s dominance of the Clearwire Board and provide a much-needed additional voice on Clearwire’s key corporate decisions.

DISH’s proposed financing terms are also superior to the Sprint Note Purchase Agreement. Under DISH’s proposal, Clearwire would still be able to draw down a maximum of $800.0 million, but it would do so at the less coercive exchange ratio of $2.50 per share, which would result in two-thirds less dilution than the terms of Sprint’s financing. In addition, DISH’s proposal would respect existing pre-emptive rights under the Clearwire Equityholders’ Agreement by allowing eligible Clearwire stockholders to avoid dilution by purchasing exchangeable notes.

Of course, although superior to Sprint’s current offer, DISH’s offer may turn out still to be inadequate for Clearwire’s stockholders. As we have said repeatedly, the battle for Clearwire is just beginning. To ensure that this ensuing battle redounds to the benefit of all Clearwire stockholders, the Board must create an open and transparent process whereby all interested parties can make offers to Clearwire’s stockholders. Only through such a competitive bidding process can all Clearwire stockholders reap the full value of their shares.

Throughout the process thus far, we believe the Special Committee has been feckless and Clearwire’s directors have failed to account for the best interests of minority stockholders. The time has come for that to end. We hereby request that you appoint a wholly new and truly independent Special Committee made up of newly appointed directors. Such a reconstitution would ensure completely fresh perspectives, and a Special Committee unencumbered by the past defaults and misjudgments of the current Special Committee—most obviously the flawed recommendations that stockholders accept clearly inadequate Sprint bids at $2.97 and $3.40 per share. The newly reconstituted Special Committee should be delegated all the powers of the Board, including decisions regarding interim financing, and specifically directed to run a fair and transparent process and evaluate all offers accordingly. We would welcome minority shareholder input on candidates to be considered for the Special Committee.

In order to consider DISH’s offer and any other offer that may be forthcoming through a competitive bidding process, the Board must recommend against the Sprint merger at tomorrow’s stockholders meeting, allow the stockholders to vote AGAINST the Sprint offer, and then terminate the merger agreement to break free from Sprint’s oppressive control. Sprint

2

obtained majority control through the Eagle River transaction, and then secured veto power over alternative transactions and financing proposals through the unfair merger agreement. Sprint has abused its controlling position, wielding it as a cudgel against fair dealing for minority stockholders. The Board must not permit those abuses to continue. Once released from Sprint’s oppressive control following the stockholders’ rejection of the Sprint offer tomorrow, the Company will be free to pursue DISH’s offer or competing bids and thus to realize the true value of Clearwire for all stockholders—not just its controlling stockholder Sprint.

3

Exhibit 3

FOR IMMEDIATE RELEASE:

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

Crest Financial Urges Clearwire Board to Recommend AGAINST Sprint Merger, Open Competitive Bidding for Clearwire, and Reconstitute Special Committee

Sends letter to Clearwire Board calling DISH’s offer “clearly superior” to Sprint’s and urging the Clearwire Board to pursue a competitive bidding process

HOUSTON, May 30, 2013 — Crest Financial Limited, the largest of the independent minority stockholders of Clearwire Corporation (NASDAQ: CLWR), today urged the Clearwire Board of Directors to reverse its recommendation on the Sprint-Clearwire merger following DISH Network Corporation’s $4.40 per share tender offer announced last night and to pursue an “open and competitive bidding process” for Clearwire. Crest also urged the Board immediately to “reconstitute the Special Committee with newly appointed, truly independent directors and empower the Special Committee with the full authority of the Board to evaluate the DISH offer and any other offer for the Company that may be made after the Board conducts a fair and transparent process that encourages these offers, and to make decisions about interim financing.”

According to David K. Schumacher, Crest’s General Counsel, “The Board has a fiduciary obligation to give full consideration to DISH’s offer, which is clearly actionable, and any other eventual offers that would trump the DISH offer. DISH’s offer for Clearwire confirms what Crest and others have been saying for months: Clearwire is the crown jewel, and the Company can realize its true value only through a competitive bidding process. DISH has initiated that process, and it is your legal obligation to pursue DISH’s offer and other potential offers now.”

Schumacher added: “The Board must encourage Clearwire’s stockholders to reject Sprint’s latest bid at tomorrow’s special meeting. Perhaps the only favorable term in the otherwise oppressive merger agreement with Sprint is the provision that you can change your recommendation and advise the stockholders to vote AGAINST the deal without paying a termination fee. You should exercise that option now. After the Clearwire stockholders accept your revised recommendation and vote AGAINST the Sprint offer, the Clearwire Board can terminate the unfair Sprint merger agreement, consider DISH’s offer, and solicit direct bids from others. Clearwire can pursue this course with the assurance that it will be able to continue operations during the competitive bidding process because Crest stands by its offer to provide the Company with $240.0 million in convertible financing, and is even willing to improve the exchange ratio to $2.50 per share (from the previous ratio of $2.00 per share) to match DISH’s proposed financing terms.”

Crest’s letter also notes: “Of course, although superior to Sprint’s current offer, DISH’s offer may turn out still to be inadequate for Clearwire’s stockholders. As we have said

repeatedly, the battle for Clearwire is just beginning. To ensure that this ensuing battle redounds to the benefit of all Clearwire stockholders, the Board must create an open and transparent process whereby all interested parties can make offers to Clearwire’s stockholders. Only through such a competitive bidding process can all Clearwire stockholders reap the full value of their shares.”

Schumacher stated: “Throughout the process thus far, we believe the Special Committee has been feckless and Clearwire’s directors have failed to account for the best interests of minority stockholders. The time has come for that to end. We hereby request that you appoint a wholly new and truly independent Special Committee made up of newly appointed directors. Such a reconstitution would ensure completely fresh perspectives, and a Special Committee unencumbered by the past defaults and misjudgments of the current Special Committee—most obviously the flawed recommendations that stockholders accept clearly inadequate Sprint bids at $2.97 and $3.40 per share. The newly reconstituted Special Committee should be delegated all the powers of the Board, including decisions regarding interim financing, and specifically directed to run a fair and transparent process and evaluate all offers accordingly. We would welcome minority shareholder input on candidates to be considered for the Special Committee.”

The letter to the Clearwire Board concludes: “In order to consider DISH’s offer and any other offer that may be forthcoming through a competitive bidding process, the Board must recommend against the Sprint merger at tomorrow’s stockholders meeting, allow the stockholders to vote AGAINST the Sprint offer, and then terminate the merger agreement to break free from Sprint’s oppressive control. Sprint obtained majority control through the Eagle River transaction, and then secured veto power over alternative transactions and financing proposals through the unfair merger agreement. Sprint has abused its controlling position, wielding it as a cudgel against fair dealing for minority stockholders. The Board must not permit those abuses to continue. Once released from Sprint’s oppressive control following the stockholders’ rejection of the Sprint offer tomorrow, the Company will be free to pursue DISH’s offer or competing bids and thus to realize the true value of Clearwire for all stockholders—not just its controlling stockholder Sprint.”

D.F. King & Co, Inc. has been retained by Crest to assist it in the solicitation of proxies in opposition to the merger. If stockholder have any questions or need assistance in voting the GOLD proxy card, please call D.F. King & Co. at (800) 949-2583. The full letter to the Clearwire Board can be found at http://www.dfking.com/clwr or http://www.bancroftpllc.com/crest.

About Crest Financial Limited

Crest Financial Limited (“Crest”) is a limited partnership under the laws of the State of Texas. Its principal business is investing in securities.

Important Legal Information

In connection with the proposed merger of Clearwire Corporation (“Clearwire”) with Sprint Nextel Corporation (the “Proposed Sprint Merger”), Crest and other persons (the

“Participants”) have filed a supplement to its definitive proxy statement with the U.S. Securities and Exchange Commission (“SEC”). The definitive proxy statement and the supplement have been mailed to the stockholders of Clearwire. SECURITYHOLDERS OF CLEARWIRE ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT AND THE SUPPLEMENT, WHICH ARE AVAILABLE NOW, AND THE PARTICIPANTS’ OTHER PROXY MATERIALS FILED WITH THE SEC WHEN THEY BECOME AVAILABLE, BECAUSE THEY CONTAIN IMPORTANT INFORMATION, INCLUDING ADDITIONAL INFORMATION RELATED TO THE PARTICIPANTS, CLEARWIRE AND THE PROPOSED SPRINT MERGER. The definitive proxy statement, the supplement and all other proxy materials filed with the SEC are available at no charge on the SEC’s website at http://www.sec.gov. In addition, the definitive proxy statement and the supplement are also available at no charge on the website of the Participants’ proxy solicitor at http://www.dfking.com/clwr.

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.

SOURCE: Crest Financial Limited