<PAGE>   1
                                                                  EXHIBIT 10.2.7

Confidential: Use of disclosure of this document is subject to the restriction
on the Confidentiality Statement.

                                    AMENDMENT

                                       TO

                        IDEN SUBSCRIBER SUPPLY AGREEMENT

                                     BETWEEN

                                 MOTOROLA, INC.

                                       AND

                           NEXTEL COMMUNICATIONS, INC.

            This Amendment is between Motorola, Inc. a Delaware corporation
       ("Motorola") and Nextel Communications, Inc. ("Customer") and amends the
iDEN Subscriber Supply Agreement dated as of November 4, 1991, as heretofore
amended, modified, supplemented or otherwise revised ("Supply Agreement").

            WHEREAS, the parties have mutually agreed to enter into this
Amendment to the Supply Agreement in order to encourage efforts to enhance the
reputation of iDEN in the United States market place by establishing improvement
plans for iDEN subscriber delivery, and

            WHEREAS, this Amendment shall set forth the Rebate Program under the
Supply Agreement.

            NOW THEREFORE, in consideration of their mutual promises set forth
herein and for other good and valuable consideration received by each of them,
the parties agree to amend the Supply Agreement by adding the following new
Sections to the Supply Agreement:

(A) Customer shall be entitled to the below stated rebate(s) upon the purchase
of the required number of subscriber units set forth below:

<TABLE>
<CAPTION>

Column  1                                  2                          3                    4
            Year            Required # of Subscriber Units          Rebate       Per Subscriber Reduction
            ----            ------------------------------          ------       ------------------------
<S>        <C>             <C>                                     <C>          <C>

            1999                           [ * ]                   [ * ]                 [ * ]
            2000                           [ * ]                   [ * ]                 [ * ]
            2001                           [ * ]                   [ * ]                 [ * ]
            2002                           [ * ]                   [ * ]                 [ * ]
            2003                           [ * ]                   [ * ]                 [ * ]

</TABLE>

             (i)              If, during the relevant year, the required number
                        of subscriber units set forth in Column 2 of the table
                        above is not reached, the rebate amount for such year
                        set out in Column 3 of the table above shall be reduced
                        on a per subscriber basis in the amount set forth in
                        Column 4 of the table above for each subscriber unit
                        that Customer falls short of [ * ] for the relevant
                        year. The Column 2 number is the minimum number of
                        subscribers to qualify for this rebate only. To the
                        extent that Customer has agreed to a higher minimum
                        purchase quantity


Motorola/Nextel                            Equipment Purchase Agreement
            * Confidential portions omitted and filed separately with the
Commission pursuant to an application for confidential treatment pursuant to
Rule 24b-2 under the Securities and Exchange Act of 1934, as amended.


<PAGE>   2
Confidential: Use of disclosure of this document is subject to the restriction
on the Confidentiality Statement.

                        during any relevant period elsewhere, then this Section
                        shall in no way modify such agreement.

            (ii)        The rebate shown in Column 2 of the table above shall be
                        the maximum rebate paid under this Amendment. Subscriber
                        shipments in excess of [ * ] in any year will not result
                        in any increase in the rebates defined above.

            (iii)       The [ * ] unit commitment per year is based upon
                        Motorola subscriber units remaining competitive in price
                        with iDEN subscriber units with similar features
                        manufactured by other parties. If at any time Customer
                        believes Motorola subscriber units are not competitive
                        with other iDEN subscriber manufacturers, Customer shall
                        notify Motorola and provide documentation of price
                        differential. The parties shall then agree on actions to
                        remedy the deficiency. If the parties can not agree on a
                        course of action to make Motorola competitive, the
                        subscriber units with similar features and comparable
                        quality manufactured by third parties shall count
                        towards the [ * ] unit commitment.

            (iv)        If, for any reason, Motorola fails to ship subscriber
                        units that were ordered by Customer (and other
                        qualifying purchasing entities) per agreed upon shipment
                        lead times in any year, the orders that Motorola failed
                        to ship shall be added to shipment quantities for the
                        purpose of meeting the [ * ] unit commitment set forth
                        in Column 2 in the above table. If Customer requests
                        such adjustment to shipment quantities in any year,
                        those units will count in the year of order and will be
                        excluded from the shipments in the subsequent year.

            (v)         Purchases by Customer of subscriber units from a
                        Motorola licensed alternate supplier of subscriber units
                        that contain at least [ * ] of their product cost value
                        from Motorola manufactured or assembled parts shall
                        count towards the required number of subscriber units
                        set forth in Column 2 above.

            (vi)        [ * ]

(B)         [ * ]

            (i)         [ * ]:

                        (a)          [ * ]
                        (b)          [ * ]
                        (c)          [ * ]
                        (d)          [ * ]
                        (e)          [ * ]

           (ii)                      [ * ]


           (iii)                     [ * ]



                                                [ * ]



Motorola/Nextel                             Equipment Purchase Agreement
            * Confidential portions omitted and filed separately with the
Commission pursuant to an application for confidential treatment pursuant to
Rule 24b-2 under the Securities and Exchange Act of 1934, as amended.



<PAGE>   3
Confidential: Use of disclosure of this document is subject to the restriction
on the Confidentiality Statement.



           (iv)                                 [ * ]

           (v)                                  [ * ]

(C) [ * ]

           (i)                                  [ * ]

           (ii)                                 [ * ]

[ * ]

The Supply Agreement shall remain in full force and effect except as expressly
amended hereby. This Amendment is effective as of January 1, 1999 with respect
to and for all purchases of subscriber units accruing on or after such date.



Motorola/Nextel                            Equipment Purchase Agreement
            * Confidential portions omitted and filed separately with the
Commission pursuant to an application for confidential treatment pursuant to
Rule 24b-2 under the Securities and Exchange Act of 1934, as amended.

<PAGE>   4

Confidential: Use of disclosure of this document is subject to the restriction
on the Confidentiality Statement.



            IN WITNESS WHEREOF, this Amendment has been executed and delivered
by the parties set forth below.

<TABLE>
<CAPTION>

<S>                                       <C>
MOTOROLA, INC.                            NEXTEL COMMUNICATIONS, INC.

By:/s/ Charles F. Wright                  By:/s/ Stephen Taylor         12/29/99
  -----------------------------              -----------------------------------
      (Authorized Signatory)                    (Authorized Signatory)

Name: Charles F. Wright                   Name: Stephen Taylor

Title: Sr. V.P. & G.M. CSG-NA             Title: V.P. - Supply Chain Management

</TABLE>



Motorola/Nextel                             Equipment Purchase Agreement

Commission pursuant to an application for confidential treatment pursuant to
Rule 24b-2 under the Securities and Exchange Act of 1934, as amended.