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                                                                   Exhibit 10.39

                                           October 13, 1999

Donald Manning, Esq.
Nextel Partners Operating Corp.
4500 Carillon Point
Kirkland, WA 98033

      Re:   Appointment of Nextel Partners Operating Corp. ("Partners") as
            Designee of Nextel WIP Corp. ("NWIP") to Perform Specified Duties
            under Section 6.9 of Joint Venture Agreement (the "JVA") dated as of
            January 29, 1999 by and among Partners, NWIP, and Nextel Partners,
            Inc. ("NPI")

Dear Don:

      This letter (the "Designation") sets forth the agreement with respect to
(i) the appointment of Partners to perform specified duties on behalf of NWIP
and as NWIP's designee under and for purposes of Section 6.9 of the JVA, and
(ii) the designation of Partners as a "Transferring Subsidiary" for purposes of
the Site Commitment Agreement (as defined below). Capitalized terms used in this
Designation but not otherwise defined herein shall have the same meanings
assigned to them in the JVA.

      o     In exercising its rights under Section 6.9 of the JVA, NWIP hereby
            authorizes and appoints Partners to perform specified duties on its
            behalf and as its designee for the sole purpose of contracting
            directly with one or more third parties (the "Contractors"),
            including Tower Asset Sub, Inc. ("Tower Sub"), to perform (subject
            to Section 6.9A of the JVA) the Site Acquisition Work and tower
            construction work referenced in Section 6.9B of the JVA
            (collectively, the "Work").

      o     The authorization and appointment set forth in the preceding
            paragraph is revocable by NWIP in its sole and absolute discretion
            upon ten (10) calendar days prior written notice to Partners;
            provided, however, that in the event NWIP exercises its right to
            revoke this Designation for convenience, NWIP, in accordance with
            and to the extent set forth in Section 6.9B of the JVA, shall be
            liable for any delays in Site Acquisition Work or construction
            caused by such revocation on and after such revocation, and any such
            delays shall constitute an Excusable Delay as set forth in Sections
            6.9B and 12.5 of the JVA.

      o     For so long as and to the extent this Designation is in effect, as
            concerns all actions taken or omitted, and all Work performed by
            Partners as designee of NWIP hereunder, Partners acknowledges and
            agrees that such actions are taken or omitted, and such Work is
            performed, by Partners in place of and in substitution for NWIP, and
            that, notwithstanding anything to the contrary in Section 6.9 of the
            JVA or any other provision of the JVA relating to liability or
            responsibility for the consequences of failure to timely and
            properly take or complete any such action or Work, (i) NWIP shall
            have no liability or responsibility of any nature whatsoever to
            Partners in connection with any such action, omission, or Work, and
            (ii) Partners' failure to timely and properly take or complete (or
            arrange for the taking or completion of) any such action or Work
            (other than because of any act of any government in its sovereign
            capacity (including zoning or licensing actions), war or
            insurrection, strike or slow down, extreme weather, fire,
            earthquake, flood, epidemic, quarantine restriction, or acts of God
            or other such occurrences or events beyond the control of Partners)
            shall not constitute an Excusable Delay for purposes of the
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Donald Manning, Esq.
October 13,1999
Page 2


            JVA or otherwise relieve or release Partners from any of its
            obligations under the JVA, including without limitation, those
            relating to the scheduled Build Out of its ESMR Network.

      o     Pursuant to this Designation and the terms of Section 2.1 of the
            Master Site Commitment Agreement (the "Site Commitment Agreement")
            dated as of April 20, 1999 among Nextel Communications, Inc., Nextel
            of New York, Inc., Nextel Communications of the Mid-Atlantic, Inc.,
            Nextel South Corp., Nextel of California, Inc., Tower Parent Corp.,
            SpectraSite Holdings, Inc., and Tower Asset Sub, Inc., Partners
            shall be designated as, and shall be deemed to be, a "Transferring
            Subsidiary" as that term is defined in the Site Commitment
            Agreement. All Work shall be arranged and/or performed strictly in
            accordance with the terms of the Site Commitment Agreement, and all
            towers that are the subject of the Work shall meet the Minimum
            Specifications of the Site Commitment Agreement, except as otherwise
            expressly consented to in writing by NWIP, which consent shall not
            be unreasonably withheld or delayed. Partners shall cause all
            Contractors engaged by it or with its authorization to perform the
            Work in compliance with this paragraph.

      o     Partners shall report monthly to NWIP on the status of the Work for
            each tower site that is or has been constructed by Partners pursuant
            to Section 6.9 of the JVA and this Designation or by Tower Sub in
            the Partner Area pursuant to the Site Commitment Agreement. Such
            report shall be in the form of Annex I attached hereto, which form
            may be modified from time to time with the mutual agreement of the
            parties. Partners shall maintain all records and information,
            including, without limitation, site leases, construction plans,
            permits, and the like, required to be maintained or provided by a
            Transferring Subsidiary under the Site Commitment Agreement. In
            addition, Partners shall provide NWIP with copies of any notices
            delivered or received by it pursuant to the Site Commitment
            Agreement and shall, on NWIP's request and at NWIP's expense,
            provide NWIP with copies of and access to any and all information
            and materials relating to Partner's performance of the Work or
            relating to the Site Commitment Agreement.

      o     Each of NPI and Partners represents and warrants that (i) it is duly
            authorized to execute, deliver, and perform its obligations under
            this Designation, (ii) no consents, authorizations, approvals, or
            notices are needed to effect the transactions contemplated by this
            Designation, and (iii) the execution, delivery, and performance by
            it of its obligations under this Designation will not contravene any
            applicable laws, rules, or regulations, and will not conflict with
            or result in any material breach of, or constitute a material
            default under, any indenture, mortgage, deed of trust, or other
            instrument or agreement to which it is a party or by which it is
            bound or to which any of its assets may be subject.

      o     For so long as and to the extent this Designation is in effect,
            Partners shall be solely liable for all costs associated with the
            Work. Nextel shall have no liability or obligation to any party,
            under the JVA, the Site Commitment Agreement, or otherwise, with
            respect to the Work, including, without limitation, any liability
            whatsoever for any delays, deficiencies or other defaults relating
            to the Work. Without limiting the generality of the foregoing, so
            long
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Donald Manning, Esq.
October 13, 1999
Page 3


            as Partners is responsible for, or is authorized to make
            arrangements with Contractors for, conducting the Work, and except
            as expressly set forth in the second paragraph of this Designation,
            Partners shall not be entitled to any remedy contemplated by Section
            6.9B of the JVA with respect to such Work. This paragraph shall
            survive the revocation or expiration of this Designation to the
            extent it relates to Work performed or in progress during the term
            of this Designation.

      o     Partners, for itself and its successors and assigns, hereby releases
            and forever discharges, and agrees to indemnify and hold harmless,
            Nextel and each of its affiliates, subsidiaries, predecessors,
            officers, directors, agents, shareholders, employees, insurers, and
            representatives from and against any and all liability, claims,
            demands, or actions in any way relating to Partners' activities as
            contemplated by this Designation or to the Work or arising from
            Partners' noncompliance with the terms and conditions of this
            Designation. NPI is and shall remain jointly and severally liable
            with Partners for the full and punctual performance of the
            indemnification obligations set forth in this paragraph. This
            paragraph shall survive the revocation or expiration of this
            Designation to the extent it relates to any acts or omissions
            arising or occurring during the term of this Designation.

      o     This Designation shall remain in effect until the earlier of (i)
            NWIP's revocation of its appointment of Partners in accordance with
            the second paragraph hereof, and (ii) the Build Stop Date.

      o     Nothing in this Designation shall be construed to create the
            relationship of partners, joint venturers, employer/employee,
            principal/agent, or any other joint enterprise.

      o     The parties each shall deliver such further documents or assurances
            as may be reasonably required by the other to effect the
            authorization and appointment contemplated hereby.

      o     Except as provided herein, the terms and conditions of the JVA shall
            remain unchanged and in full force and effect.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
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Donald Manning, Esq.
October 13,1999
Page 4


      Please indicate your acceptance of the foregoing by causing this letter to
be signed by a duly authorized representative and returned to me at your
earliest convenience.


                                        NEXTEL WIP CORP.

                                        By: /s/ Alan Strauss
                                           -------------------------------------
                                        Name: Alan Strauss
                                             -----------------------------------
                                        Title: Vice President
                                              ----------------------------------


ACCEPTED AND AGREED:

NEXTEL PARTNERS
  OPERATING CORP.

By: /s/ Donald J. Manning
   --------------------------------
Name: Donald J. Manning
     ------------------------------
Title: Vice President
      -----------------------------


ACCEPTED AND AGREED:

NEXTEL PARTNERS, INC.

By: /s/ Donald J. Manning
   --------------------------------
Name: Donald J. Manning
     ------------------------------
Title: Vice President
      -----------------------------