Document:

<PAGE>

                                                                   Exhibit 10.21

                              AMENDMENT AND CONSENT

     THIS AMENDMENT AND CONSENT (this "Amendment") is made and entered into as
of the 1st day of February, 2005 by and among Clearwire Corporation, a Delaware
corporation, f.k.a. Flux U.S. Corporation ("Clearwire"), ITFS Spectrum Advisors
LLC, a Delaware limited liability company ("ISA"), and ITFS Spectrum Consultants
LLC, a Delaware limited liability company ("ISC").

                                    RECITALS

     A. Clearwire and ISA are parties to that certain Warrant Agreement dated
November 13, 2003 ("Warrant Agreement") pursuant to which ISA agreed to
introduce Clearwire to third parties and to facilitate an acquisition of ITFS,
MDS and MMDS spectrum through lease or purchase from such parties, and Clearwire
agreed in connection with such acquisitions or leases to grant to ISA warrants
to purchase shares of Class A common stock of Clearwire ("Warrants") as
consideration for ISA's services.

     B. Clearwire and ISC intend to enter into a Spectrum Acquisition Consulting
Agreement ("Consulting Agreement") whereby at such time as ISA has earned all
available compensation under the Warrant Agreement, ISC will provide
introduction and facilitation services to Clearwire for the acquisition or lease
of ITFS, MDS and MMDS spectrum and Clearwire will pay ISC the Consulting
Compensation (defined in the Consulting Agreement) upon the satisfaction of
certain conditions, including that ISC facilitate the execution of definitive
agreements and, with respect to a license purchase, lease or sublease, and the
closing of the transaction with such third party as requested by Clearwire (an
"ISC Acquisition").

     C. Notwithstanding the fact that the Consulting Agreement does not become
effective until such time as ISA has earned all available compensation under the
Warrant Agreement, ISC wishes to provide that, upon its request, acquisitions or
leases of ITFS, MDS or MMDS spectrum that Clearwire closes which originates from
introductions made by Daryl Coffee, as an authorized agent of ISC, be deemed ISC
Acquisitions, rather than ISA Acquisitions, and such transactions be treated as
such under the Consulting Agreement.

                                    AGREEMENT

     In consideration of the premises, the mutual covenants and promises made
below, and other good and valuable consideration, the parties agree as follows:

     1. Amendment to Warrant Agreement. The Warrant Agreement shall be amended
to include a new Section 2.7 as follows:

     SECTION 2.7. RELATIONSHIP TO ISA. Notwithstanding anything to the contrary
in this Agreement, ITFS Spectrum Consultants LLC ("ISC"), may, upon written
notice to ISA and Clearwire, elect to have Acquisitions for up to 25,000,000
CPOPS (as defined in the Consulting Agreement), that are closed between
Clearwire and licensees of ITFS, MDS, or MMDS channels which Acquisitions
originated from the introduction of Clearwire to the license holder by Daryl
Coffee, in his capacity as an authorized agent of ISC (collectively, the
"Excluded Transactions")

<PAGE>

treated as an Acquisition under the Consulting Agreement. ISA agrees that it
shall have no right to demand or receive Warrants or other consideration in
connection with the Excluded Transactions.

     2. Counterparts. This Amendment may be executed in one or more
counterparts, all of which shall be considered one and the same agreement and
shall become effective when one or more counterparts have been signed by each of
the parties and delivered to the other parties.

     3. Entire Agreement. This Amendment constitutes the entire agreement
between the parties, and supersedes all prior agreements and understandings,
both written and oral, among the parties with respect to the subject matter of
this Amendment. Except as expressly provided in this Amendment, all other terms
and conditions of the Warrant Agreement, including all exhibits, schedules and
appendices thereto, remain in full force and effect and are not amended or
modified in any respect.

                     [Signatures are on the following page]

                                        2

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed or caused this
Amendment to be executed and delivered by their duly authorized officers, as of
the day and year first above written.

                                        ITFS Spectrum Advisors LLC

                                        By: /s/ Rudolph J. Geist
                                            ------------------------------------
                                        Name: Rudolph J. Geist
                                        Title: Managing Member

                                        ITFS Spectrum Consultants LLC

                                        By: /s/ Rudolph J. Geist
                                            ------------------------------------
                                        Name: Rudolph J. Geist
                                        Title: Managing Member

                                        Clearwire Corporation

                                        By: /s/ Benjamin G. Wolff
                                            ------------------------------------
                                        Name: Benjamin G. Wolff
                                        Title: Executive Vice President

                                        3<PAGE>

                                                                   Exhibit 10.22

                          SECOND AMENDMENT AND CONSENT

     THIS SECOND AMENDMENT AND CONSENT (this "Amendment") is made and entered
into as of the 26 day of April 2006 by and among Clearwire Corporation, a
Delaware corporation, f.k.a. Flux U.S. Corporation ("Clearwire"), and ITFS
Spectrum Consultants LLC, a Delaware limited liability company ("ISC").

                                     RECITAL

     Clearwire and ISC are parties to that certain Spectrum Acquisition
Consulting Agreement dated February 1, 2005 ("SACA") pursuant to which ISC
agreed to introduce Clearwire to third parties and to facilitate the acquisition
of ITFS, MDS and MMDS spectrum through lease or purchase from such parties, and
Clearwire agreed in connection with such acquisitions or leases to grant to ISC
Consulting Consideration (defined in the SACA) upon the satisfaction of certain
conditions, including that ISC facilitate the execution of definitive agreements
and, with respect to a license purchase, lease or sublease, the closing of the
transaction with such third party as requested by Clearwire.

                                    AGREEMENT

     In consideration of the premises, the mutual covenants and promises made
below, and other good and valuable consideration, the parties agree as follows:

     1. Amendments to SACA. The SACA shall be amended as follows:

     A. SECTION 1(B) shall be amended by deleting the term "Consulting
Compensation" in the first sentence and replacing such term with "Consulting
Consideration."

     B. SECTION 3(B) shall be deleted in its entirety and shall be replaced with
the following new Section 3(b):

          "(b) CALCULATION OF CONSULTING CONSIDERATION. The consulting
     consideration ("Consulting Consideration") payable shall be calculated by
     multiplying the number of CPOPs in the applicable geographic service area
     ("GSA") times the applicable "Per CPOP ISC Consideration" determined as
     follows:

          (i) For the markets listed on Schedule 3(b)(i):

                                   Per CPOP ISC
                                  Consideration
                                  -------------
                                      $0.025

          (ii) For the Acquisition reflected in that certain EBS Excess Capacity
     Use and Royalty Agreement by and between Clearwire Spectrum Holdings LLC
     and District Board of Trustees of Valencia Community College, Florida:

<PAGE>

                                   Per CPOP ISC
                                  Consideration
                                  -------------
                                      $0.005

          (iii) For all other markets:

<TABLE>
<CAPTION>
                                  If Clearwire's
If Clearwire's Acquisition     Acquisition Price is
 Price is Up to $1.50 per     Equal to or More Than
    CPOP, Per CPOP ISC       $1.50 per CPOP, Per CPOP
   Consideration Equals      ISC Consideration Equals
--------------------------   ------------------------
<S>                          <C>
           $0.02                       $0.01
</TABLE>

     With respect to any Acquisition, the Per CPOP ISC Consideration shall be
defined and calculated on the following basis:

          (iv) The parties shall use the average number of households located
     within the GSA as defined under FCC rules for each channel group (or
     individual channel in the case of an Acquisition of a single channel,
     either hereafter a "Channel Group") subject to the Acquisition in
     determining the appropriate number of CPOPs for purposes of payment of the
     Consulting Consideration for each Channel Group (as represented by an
     individual FCC call sign), notwithstanding the potential of interference
     thereto from neighboring channels (the "Method"). GSA CPOP amounts for the
     Pending Transactions as of the effective date of this Agreement are
     reflected on Exhibit A hereof.

          (v) In the event of a dispute over the correct number of households
     located within a GSA for a Channel Group other than those provided on
     Exhibit A, the parties agree to determine the correct number of households
     using the most up-to-date commercial engineering software generally used by
     Clearwire for calculating such household numbers for such GSAs as
     determined under the then current FCC rules."

     C. The second sentence of SECTION 3(F) shall be deleted in its entirety and
shall be replaced by the following sentence:

     "Upon the Closing of such Post-Termination Acquisition, Clearwire will pay
to ISC consideration at a rate equal to the amount determined pursuant to
Section 3(b)(iii) for each Post-Termination Acquisition ("Post-Termination
Consideration")."

     D. The first clause of the first sentence of SECTION 5 shall be amended as
follows:

     "This Agreement shall commence and become effective as of the Effective
Date and shall continue until the earlier of (i) March 17, 2007,...."

                                        2

<PAGE>

     2. Counterparts. This Amendment may be executed in one or more
counterparts, all of which shall be considered one and the same agreement and
shall become effective when one or more counterparts have been signed by each of
the parties and delivered to the other parties.

     3. Entire Agreement. This Amendment constitutes the entire agreement
between the parties, and supersedes all prior agreements and understandings,
both written and oral, among the parties with respect to the subject matter of
this Amendment. Except as expressly provided in this Amendment, all other terms
and conditions of the SACA, including all exhibits, schedules and appendices
thereto, remain in full force and effect and are not amended or modified in any
respect.

                     [Signatures are on the following page]

                                        3

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed or caused this
Amendment to be executed and delivered by their duly authorized officers, as of
the day and year first above written.

                                        ITFS Spectrum Consultants LLC

                                        By: /s/ Rudolph J. Geist
                                            ------------------------------------
                                        Name: Rudolph J. Geist
                                        Title: Managing Member

                                        Clearwire Corporation

                                        By: /s/ Benjamin G. Wolff
                                            ------------------------------------
                                        Name: Benjamin G. Wolff
                                        Title: Co-President

                                        4

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00114-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00114-of-00352.parquet"}]]