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. 14)*

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 20, 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. 14 (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”) and Amendment No. 13 filed on May 17, 2013 (“Amendment No. 13”).

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

On May 20, 2013, CFL made available a letter to stockholders of the Issuer (the “Letter to Stockholders”), sent a letter to the board of directors of the Issuer (the “Letter to the Board”) and issued a press release relating to both (the “Press Release”). In the Letter to Stockholders and the Letter to the Board, CFL stated its belief that the Issuer should remain an independent company while the contest for control of Sprint Nextel Corporation (“Sprint”) is resolved, and that Issuer’s stockholders should therefore vote against the proposed merger of the Issuer with Sprint. A copy of the Letter to Stockholders is attached hereto as Exhibit 2, a copy of the Letter to the Board is attached hereto as Exhibit 3 and a copy of the Press Release is attached hereto as Exhibit 4, each of which are incorporated herein by reference. The descriptions herein of the Letter to Stockholders, the Letter to the Board and the Press Release are qualified in their entirety by reference to the Letter to Stockholders, the Letter to the Board and the 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 Letter to Stockholders attached hereto as Exhibit 2, the Letter to the Board attached hereto as Exhibit 3, the Press Release attached hereto 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 20, 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 20^th day of May, 2013.

Exhibit 2

CREST FINANCIAL LIMITED

JPMorgan Chase Tower

600 Travis, Suite 6800

Houston, Texas 77002

May 20, 2013

Dear Fellow Clearwire Stockholders:

In our letters dated May 15 and May 17, 2013, Crest Financial Limited (“Crest”) explained a number of reasons why you should vote AGAINST the proposed merger (the “Sprint-Clearwire Merger”) of Clearwire Corporation (“Clearwire” or the “Company”) with Sprint Nextel Corporation (“Sprint”). As we said in those letters and on other occasions, Sprint’s offer grossly undervalues Clearwire and its spectrum assets.

We write today to emphasize that your focus of attention should not be on what happens at the Clearwire stockholders meeting on May 21st but rather on what will ultimately happen with the contest for Sprint in June.

We believe that Clearwire should not be locked up before the battle for control of Sprint is resolved. Clearwire is the key reason for the push by DISH and SoftBank to acquire control of Sprint. Letting Sprint gobble up Clearwire now would only transfer Clearwire’s value to Sprint. Conversely, keeping Clearwire in play while the contest for Sprint is pending drives both bidders for Sprint to focus on Clearwire. So long as Clearwire is not locked up, the winner of Sprint is not guaranteed Clearwire and the loser of Sprint is not precluded from making a play for Clearwire. And a third player, like Verizon, could enter the contest for Clearwire.

Thus, our letter last week highlighted the potential scenarios following the contest for Sprint. The key is to preserve Clearwire as a freestanding company before the Sprint contest is settled, so that the real battle for Clearwire can begin. Regardless whatever the Clearwire Board has done up to now, it needs to recognize this current dynamic and not compound error upon mistake by letting Sprint lock up Clearwire prior to the determination of who will own Sprint.

And in a separate letter today to Clearwire Board Chairman John W. Stanton, we explained that the Board of Clearwire may now have an opportunity to pursue a competitive process that protects minority stockholders and realizes the true value of Clearwire and its assets. We have also urged the Clearwire Board not to accept any revised Sprint offer, not to postpone or adjourn Tuesday’s stockholder meeting, and not to consider any future offer for Clearwire that does not include adequate protections for minority stockholders—similar to those Sprint has offered its own stockholders.

Clearwire is the crown jewel, and Sprint is only the intermediary. There is no reason to let Sprint lock up Clearwire before Sprint’s ownership is settled. The stockholders and Board of Clearwire should reject all offers from Sprint until the contest for Sprint is decided. Then the competition for Clearwire can begin in earnest between the winner or loser of Sprint, or another third party.

*    *    *

For all of the foregoing reasons as well as the reasons stated in Crest’s proxy materials, we urge you to vote “AGAINST” the Sprint-Clearwire Merger by signing and returning the GOLD proxy card.

Crest urges all stockholders NOT to sign or return any WHITE proxy card sent to you by the Company.

If you have already returned the WHITE proxy card, you can effectively revoke it by voting the GOLD proxy card. The GOLD proxy card will provide instructions on how to vote on-line. Only your latest-dated proxy card or vote will be counted.

If you have any questions or need assistance in voting the GOLD proxy card, please contact our proxy solicitor, D.F. King & Co., Inc. at 1-800-949-2583 (toll-free). To access Crest’s definitive proxy statement at no charge, please visit the following website: http://www.dfking.com/clwr.

Sincerely yours,

/s/ David K. Schumacher

David K. Schumacher

General Counsel

Crest Financial Limited

*************************************************************************************

About 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 Sprint-Clearwire Merger, Crest and other persons (the “Participants”) have filed a definitive proxy statement with the U.S. Securities and Exchange Commission (“SEC”). The definitive proxy statement has been mailed to the stockholders of Clearwire. SECURITYHOLDERS OF CLEARWIRE ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT AND ALL OTHER PROXY MATERIALS FILED WITH THE SEC, BECAUSE THEY CONTAIN IMPORTANT INFORMATION, INCLUDING ADDITIONAL INFORMATION RELATED TO THE PARTICIPANTS, CLEARWIRE, AND THE SPRINT-CLEARWIRE MERGER. The definitive proxy statement 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 is also available at no charge on the website of the Participants’ proxy solicitor at http://www.dfking.com/clwr.

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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.

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Exhibit 3

CREST FINANCIAL LIMITED

JPMorgan Chase Tower

600 Travis, Suite 6800

Houston, Texas 77002

May 20, 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”) last week wrote the stockholders of Clearwire Corporation (“Clearwire” or the “Company”) to emphasize that their focus should be on what happens with the battle between SoftBank Corporation (“Softbank”) and DISH Network Corporation (“DISH”) for control of Sprint Nextel Corporation (“Sprint”). Before control of Sprint is resolved, Clearwire should not be locked up. This is because allowing Sprint to acquire Clearwire now would only transfer Clearwire’s value to Sprint. But waiting for the SoftBank-DISH-Sprint process to conclude would permit SoftBank and DISH to compete directly for Clearwire—and allow you, as required by your fiduciary duties, to deliver Clearwire’s value to all stockholders and not just Sprint.

Given this clear dynamic, if the vote is against the Sprint-Clearwire merger, you should not accept any revised offer from Sprint until after Sprint’s ownership is resolved. And you should not postpone or adjourn Tuesday’s stockholder meeting or consider any revised offers from Sprint unless and until you negotiate minority protections that are missing from the current Merger Agreement. Those terms protecting minority stockholders should be at least as favorable as the terms the Sprint Board has secured for Sprint’s stockholders and is now pointing to in order to win over the SoftBank bid. (See Sprint-SoftBank Merger Investor Presentation (May 2013).)

For example, you should obtain the following for the Clearwire stockholders (which are the same as the terms Sprint has proposed for its own shareholders):

Any attempt by Sprint to postpone or adjourn the vote or revise the deal will afford you the opportunity to stop and start over, and use this time to pursue a competitive process that can protect minority stockholders and unlock the true value of Clearwire. There is no reason to let Sprint lock up Clearwire before Sprint’s ownership is settled. You should reject all offers from Sprint until the contest for Sprint is done and insist on adequate protection for Clearwire’s minority stockholders when you negotiate any revised agreement with Sprint, or any agreement with another party.

Only by acting in this way can you ensure a competitive process for Clearwire and fulfill your fiduciary duties to minority stockholders.

Sincerely yours,

/s/ David K. Schumacher

David K. Schumacher

General Counsel

Crest Financial Limited

*************************************************************************************

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 definitive proxy statement with the U.S. Securities and Exchange Commission (“SEC”). The definitive proxy statement has been mailed to the stockholders of Clearwire. SECURITYHOLDERS OF CLEARWIRE ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT, WHICH IS 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 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 is 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

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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.

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Exhibit 4

FOR IMMEDIATE RELEASE:

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

Crest Financial Urges Clearwire Stockholders to Focus on Battle for Control of Sprint

HOUSTON, May 20, 2013—Crest Financial Limited, the largest of the independent minority stockholders of Clearwire Corporation (NASDAQ: CLWR), sent separate letters today to Clearwire stockholders and John W. Stanton, Chairman of the Clearwire Board, emphasizing that the contest for control of Sprint should be resolved before any definitive action on Clearwire. The focus of the stockholders’ attention should not be on what happens at the Clearwire special meeting on May 21 but rather on what will ultimately happen with the contest for Sprint in June.

In its letter to Clearwire stockholders, Crest stated that “Clearwire should not be locked up before the battle for control of Sprint is resolved. Clearwire is the key reason for the push by DISH and SoftBank to acquire control of Sprint. Letting Sprint gobble up Clearwire now would only transfer Clearwire’s value to Sprint. Conversely, keeping Clearwire in play while the contest for Sprint is pending drives both bidders for Sprint to focus on Clearwire. So long as Clearwire is not locked up, the winner of Sprint is not guaranteed Clearwire and the loser of Sprint is not precluded from making a play for Clearwire. In addition, a third player, like Verizon, could enter the contest for Clearwire.”

Crest continued: “The key is to preserve Clearwire as a freestanding company before the Sprint contest is settled, and then the real battle for Clearwire begins. Regardless whatever the Clearwire Board has done up to now, it needs to recognize this current dynamic and not compound error upon mistake by letting Sprint lock up Clearwire, at any price, prior to the determination of who will own Sprint.”

According to David Schumacher, General Counsel of Crest, “Clearwire is the crown jewel, and Sprint is only the intermediary. There is no reason to let Sprint lock up Clearwire before Sprint’s ownership is settled. The stockholders and Board of Clearwire should reject all offers from Sprint until the contest for Sprint is decided. Then the competition for Clearwire can begin in earnest between the winner or loser of Sprint, or another third party.”

In his separate letter to Clearwire Chairman Stanton, Mr. Schumacher urged the Clearwire Board not to accept any revised Sprint offer, not to postpone or adjourn Tuesday’s stockholder meeting, and not to consider any future offer for Clearwire that does not include adequate protections for minority stockholders. Mr. Schumacher

stated: “Any attempt by Sprint to postpone or adjourn the vote or revise the deal will afford the Clearwire Board the opportunity to stop and start over, and use this time to pursue a competitive process that can protect minority stockholders and unlock the true value of Clearwire.”

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 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 definitive proxy statement with the U.S. Securities and Exchange Commission (“SEC”). The definitive proxy statement has been mailed to the stockholders of Clearwire. SECURITYHOLDERS OF CLEARWIRE ARE URGED TO READ THE DEFINITIVE PROXY STATEMENT, WHICH IS 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 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 is 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.