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                                                                 Exhibit 10.15.4


                    NON-NEGOTIABLE UNSECURED PROMISSORY NOTE



     $500,000.00                                                  March 10, 1999



     FOR VALUE RECEIVED, Daniel F. Akerson, an individual residing at 1100 Mill
Ridge, McLean, Virginia 22102 ("Executive"), promises to pay to Unrestricted
Subsidiary Funding Company, a Delaware corporation ("USF Co."), or to any
corporation controlled by Nextel Communications, Inc., a Delaware corporation
("NCI") and the parent of USF Co., that is designated by USF Co. (USF Co. or
its designee, the "Company") at its offices located at 1505 Farm Credit Drive,
McLean, Virginia 22102 (or at such other location as the Company may advise
Executive in writing prior to the relevant payment date(s)), the principal sum
of Five Hundred Thousand Dollars ($500,000.00), in lawful money of the United
States, together with simple interest at an annual rate of 4.75%, calculated on
the basis of a 360 day year having twelve equal 30 day months.  Accrued
interest shall be payable annually on each March 10 (beginning March 10, 2000)
and the entire principal amount hereof, together with all accrued and unpaid
interest thereon (from and including the most recent interest payment date to
and excluding the date of payment thereof), shall be due and payable in full on
March 10, 2002 (the "Due Date"), unless such amounts shall have been forgiven,
and Executive shall have been discharged from his payment obligations
hereunder, prior to such Due Date as provided below.  Executive shall be
entitled to make any prepayment and/or partial payment of any principal and/or
interest amount due under this Note at any time without needing to seek or
obtain the consent of the Company thereto, and the amounts due under this Note,
and accrual of interest thereon, if relevant, shall be appropriately adjusted
to reflect any such prepayment or partial payment, as the case may be.

     If Executive's employment by NCI should be terminated prior to the Due
Date for any reason, including, without limitation, voluntarily by Executive,
or by NCI with or without cause, then the entire principal amount outstanding
hereunder as of the time of such termination of employment, and all accrued and
unpaid interest thereon, shall be forgiven completely and unconditionally
(subject to Executive's obligations to satisfy any


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tax liability arising from or relating to such forgiveness of amounts due
hereunder, as provided below), automatically and without need of any action on
the part of either Executive or the Company, and thereupon Executive shall be
discharged from all other or further payment obligations hereunder of any type,
character or amount. In consideration of such forgiveness and discharge,
Executive agrees to be solely responsible for, and to hold each of the Company
and NCI harmless from and against, any federal, state, local or other income or
other tax liability that arises upon or by reason of the forgiveness of any
amounts due on or in respect of this Note.

     This Note is an unsecured obligation of Executive, is non-negotiable (but
shall be assignable by USF Co., without the need to seek or obtain Executive's
consent, to any entity designated by USF Co. as the Company), shall be binding
on and inure to the benefit of Executive, his heirs, administrators, executors
and legatees, and shall be binding on and inure to the benefit of the Company
and its successors.

     Executive hereby waives presentment for payment, notice of dishonor,
protest and notice of protest.  This Note is executed by Executive in, and
shall be subject to and governed by the internal substantive laws (without
regard to principles of conflicts or choices of laws thereof) of, the
Commonwealth of Virginia.

     IN WITNESS WHEREOF, Executive has executed and delivered, and the Company
has acknowledged and delivered, this Note on the date first above written.


     /s/ Daniel F. Akerson
     ----------------------------
     Daniel F. Akerson

                                         Acknowledged:

                              UNRESTRICTED SUBSIDIARY FUNDING COMPANY


                              By: /s/ Thomas J. Sidman
                                  --------------------------------
                                  Thomas J. Sidman, Vice President