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                                                                 Exhibit 10.17.6
                                                                 ---------------


                               IWO Holdings, Inc.
                      Independent Wireless One Corporation
                            319 Great Oaks Boulevard
                             Albany, New York 12203



                              August 24, 2000

Mr. Solon Kandel
592 Ashwood Drive
Springfield, New Jersey  07081

     Re: Stock Option Agreement, dated as of December 20, 1999 (the "Stock
         Option Agreement"), between IWO Holdings, Inc. ("Holdings") and you;
         Warrant, dated December 20, 1999, to Purchase Shares of Class B Common
         Stock of IWO Holdings, Inc. granted to you (the "Warrant"); Management
         Bonus Stock Purchase Agreement, dated as of December 20, 1999 between
         Holdings, IWO Holdings Limited and you (the "Management Stock Purchase
         Agreement"); and Employment Agreement, dated as of December 20, 1999
         (the "Employment Agreement"), among Holdings, Independent Wireless One
         Corporation ("IWO") and you.

Dear Sol:

     With reference to the above agreements, this letter agreement sets forth
certain understandings reached between Holdings, IWO and you.

     1.  Attached hereto as Exhibit A is a true and correct copy of the Stock
Option Agreement.  Such Stock Option Agreement shall be amended as follows:

     (a) Section 1 shall be amended by deleting the definitions of "Approved
Sale" and "Initial Public Offering" and replacing such definitions with the
following definitions:

          "Approved Sale" means a transaction or a series of related
           -------------
          transactions other than a Designated Merger:  (i) including, but not
          limited to, by way of merger or consolidation, which results in any
          "person" or "group" (as such terms are used in Sections 13(d) and
          14(d) of the Exchange Act or any successor provisions to either of the
          foregoing), other than (A) any one or more of the Initial Stockholders
          or Affiliates thereof or (B)  a non-U.S. entity with respect to which
          an Initial Stockholder or Affiliate thereof has an administrative
          relationship, becoming the "beneficial owner" (as defined in Rule 13d-
          3 under the Exchange Act), directly or indirectly, of a majority of
          the total voting power of the capital stock of Holdings or otherwise
          able to elect a majority of the board of directors of Holdings (for
          purposes of this definition, such person or group shall be deemed to
          beneficially own capital stock of Holdings that is held by any other
          corporation so long as such person or group beneficially owns,
          directly or indirectly, in the aggregate a majority of the total
          capital stock of such
<PAGE>

          other corporation); or (ii) which results in the sale, transfer,
          assignment, lease, conveyance or other disposition, directly or
          indirectly, of all or substantially all the assets of Holdings and its
          subsidiaries, considered as a whole (other than to an Affiliate
          thereof).

          "Initial Public Offering" means the sale of any of the common stock of
           -----------------------
          Holdings or the issuance of common stock of any Person in exchange for
          100% of the capital stock of Holdings pursuant to a registration
          statement that has been declared effective under the Act, if following
          such sale or exchange (i) the issuer is a reporting company under
          Section 12(b) or 12(g) of the Securities Exchange Act of 1934, as
          amended, and (ii) such stock is traded on the New York Stock Exchange
          or the American Stock Exchange, or is quoted on the Nasdaq National
          Market System or is traded or quoted on any other national stock
          exchange or national securities system.

     (b)  Section 1 shall be amended further by adding the following definition:

          "Designated Merger" means a transaction that results in the merger,
           -----------------
          consolidation or amalgamation of Holdings with or into any Person that
          results in the conversion of the outstanding shares of capital stock
          of Holdings into shares of capital stock of such Person (or its
          Affiliate) and such Person (or its Affiliate) has an affiliation with
          Sprint Spectrum L.P (or its Affiliates) similar to the affiliation
          between IWO and Sprint Spectrum L.P and its Affiliates (other than
          with respect to the territory covered).

     (c)  Section 3 shall be amended to add the following new clause (c):

          "(c)  Notwithstanding Section 3(a) and Section 3(b), upon the
          occurrence of a Designated Merger, the schedule set forth in Section
          3(a) shall not apply with respect to 20% of the Time Vesting Options
          that are not yet exercisable (and shall continue to apply to the
          remaining 80% of such options) and such 20% of such Time Vesting
          Options shall become fully vested and exercisable immediately prior to
          the closing of such Designated Merger."

     (d)  Section 4 (b) shall be amended by deleting such section in its
entirety and replacing such section with the following:

          "(b)  The unexercisable portion of the Time Vesting Option shall
          expire on the earlier to occur of (i) except to the extent provided in
          Section 3(b) and Section 3(c), the Termination Date or (ii) except to
          the extent provided in Section 3(b), Section 3(c) and Section 6(a), an
          Approved Sale or a Designated Merger."

     (e)  Section 6(a) shall be amended by deleting such section in its entirety
and replacing such section with the following:

                                       2
<PAGE>

          "(a)  In the event of an Approved Sale or a Designated Merger, the
          unexercised portion of the Option shall terminate upon such Approved
          Sale or Designated Merger unless (i) provision is made in writing in
          connection with such Approved Sale or Designated Merger for the
          assumption of such Options, or for the substitutions of such Options
          of new awards covering the securities of a successor entity or an
          Affiliate thereof, with appropriate adjustments as to the number and
          kind of securities and exercise prices, in which event such
          outstanding Options shall continue or be replaced, as the case may be,
          in the manner and under the terms so provided; or (ii) the Board of
          Directors otherwise shall provide in writing for such adjustments as
          it deems appropriate in the terms and conditions of the then-
          outstanding Options, including without limitation (A) accelerating the
          vesting of outstanding Options and/or (B) providing for the
          cancellation of Options and their automatic conversion into the right
          to receive the securities, cash or other consideration that a holder
          of the shares underlying such Options would have been entitled to
          receive upon consummation of such Approved Sale or Designated Merger
          had such shares been issued and outstanding immediately prior to the
          closing date of the Approved Sale or Designated Merger (net of the
          appropriate option exercise prices).  If pursuant to this Section 6(a)
          the Options are to terminate upon an Approved Sale or Designated
          Merger without provision for any of the actions described in clause
          (i) or (ii) above, then the Optionee shall be given at least ten (10)
          days' prior notice of the proposed Approved Sale or Designated Merger
          and shall be entitled to exercise such exercisable but unexercised
          portion of the Option (including all options that become exercisable
          immediately prior to the Approved Sale pursuant to Section 3(b) or the
          Designated Merger pursuant to Section 3(c)(i)) at any time during such
          ten (10) day period up to and until the close of business on the day
          immediately preceding the date of consummation of such Approved Sale
          or Designated Merger, and, notwithstanding Section 7 hereof, the
          Exercise Price may, at the option of the Optionee, be paid in whole or
          in part by delivery of shares of the Class B Common Stock owned by the
          Optionee (the value of such shares delivered as payment of the
          Exercise Price shall be determined based on and consistent with the
          value of the consideration to be tendered in connection with such
          Approved Sale or Designated Merger), and upon exercise of the Option
          the Option Shares shall be treated in the same manner as the shares of
          any other holder of Class B Common Stock."

     2.  Attached hereto as Exhibit B is a true and correct copy of the
Employment Agreement.

     (a) You agree that in the case of a Designated Merger (as defined in
Section 1(b) hereof), the obligations of the parties under the Employment
Agreement with respect to the first two sentences of Section 2(a) thereof will
be satisfied if you serve as Chief Operating Officer of the entity ("Parent")
issuing shares of its capital stock in connection with such Designated

                                       3
<PAGE>

Merger and perform such duties as are appropriate to such office as may be
assigned to you by the board of directors of Parent.

     (b) You agree that in the case of a Designated Merger, and if so requested
by Parent, you will relocate to a new residence in the vicinity of the
headquarters of Parent no later than the later of August 31, 2001 or the date
occurring six months following the closing of such Designated Merger (the
"Transition Period").  In such event, for the Transition Period or, if earlier,
until the date you acquire a new residence in the vicinity of Parent, IWO will
lease on your behalf an executive residential quarters at a cost no greater than
$2,500.00 per month.  You shall also be paid or reimbursed for reasonable
expenses incurred by you in commuting to and from such quarters to your existing
home no more frequently than twice per month during the Transition Period.  In
addition, in the case of Holdings entering into such merger agreement, you agree
to enter into the Relocation Expense Agreement attached as Exhibit C, pursuant
to which IWO will provide to you approximately $100,000 of relocation money
subject to the terms and conditions contained therein.

     3.  Attached hereto as Exhibit D is a true and correct copy of the Warrant.
Such Warrant shall be amended as follows:

     (a) The words "or Panthers Merger" shall be inserted at the end of the
parenthetical clause in the heading thereof (appearing below the legend);

     (b) The words "or upon a Panthers Merger" shall be added to the end of the
first sentence in the first full paragraph following the heading thereof;

     (c) Section 1 shall be amended by deleting the definition of "Approved
Sale" and replacing such definition with the following definition:

          "Approved Sale" means a transaction or a series of related
           -------------
          transactions other than a Panthers Merger:  (i) including, but not
          limited to, by way of merger or consolidation, which results in any
          "person" or "group" (as such terms are used in Sections 13(d) and
          14(d) of the Exchange Act or any successor provisions to either of the
          foregoing), other than (A) any one or more of the Initial Stockholders
          or Affiliates thereof or (B)  a non-U.S. entity with respect to which
          an Initial Stockholder or Affiliate thereof has an administrative
          relationship, becoming the "beneficial owner" (as defined in Rule 13d-
          3 under the Exchange Act), directly or indirectly, of a majority of
          the total voting power of the capital stock of Holdings or otherwise
          able to elect a majority of the board of directors of Holdings (for
          purposes of this definition, such person or group shall be deemed to
          beneficially own capital stock of Holdings that is held by any other
          corporation so long as such person or group beneficially owns,
          directly or indirectly, in the aggregate a majority of the total
          capital stock of such other corporation); or (ii) which results in the
          sale, transfer, assignment, lease, conveyance or other disposition,
          directly or indirectly, of all or substantially all the assets of
          Holdings and its subsidiaries, considered as a whole (other than to an
          Affiliate thereof).

                                       4
<PAGE>

     (d)  Section 1 shall be amended further by adding the following definition:

          "Panthers Merger" means a transaction that (i) results in the merger,
           ---------------
          consolidation or amalgamation or other business combination of
          Holdings with or into an entity referred to by Holdings as "Panthers,"
          or the sale, transfer, assignment, lease, conveyance or other
          disposition, directly or indirectly, of all or substantially all the
          assets of Holdings and its subsidiaries, considered as a whole, to
          Panthers, and (ii) closes prior to March 31, 2001.

     (e) Section 2(a)(ii) shall be amended to delete the "or" at the end of
Section 2(a)(ii).

     (f) Section 2(a)(iii) shall be amended to replace the "." at the end of
Section 2(a)(iii) with "; or".

     (g) Section 2(a) shall be amended to add the following new clause (iv):

         "(iv)  immediately prior to the closing of a Panthers Merger."

     (h) Section 2(b)(ii) shall be amended to delete the "or" at the end of
Section 2(b)(ii).

     (i) Section 2(b)(iii) shall be amended to replace the "." at the end of
Section 2(b)(iii) with "; or".

     (j) Section 2(b) shall be amended to add the following new clause (iv):

         "(iv)  immediately prior to the closing of a Panthers Merger."

     (k) Section 2(c) shall be amended by deleting such section in its entirety
and replacing such section with the following:

         "(c)  Holdings shall give to the Holder written notice (the "Holdings
                                                                      --------
         Notice") of the occurrence of an Approved Sale or a Panthers Merger at
         ------
         least 20 days prior to the anticipated closing of such Approved Sale
         or Panthers Merger or an Initial Investors Cash-Out within 100 days
         following such Initial Investors Cash-Out."

     (l) Section 2(f) shall be amended by deleting such section in its entirety
and replacing such section with the following:

          "(f)  (i) If the Holdings Notice is with respect to a Panthers Merger,
          the Holder shall notify Holdings on or before five days prior to the
          anticipated closing date of such Panthers Merger of such Holder's
          exercise; (ii) with respect to an Approved Sale, if the Holdings
          Notice states that Holdings anticipates that such event will cause the
          vesting of the 40% IRR Warrant or the 60% IRR Warrant, the Holder
          shall notify Holdings on or before five days prior to the anticipated
          closing date of such Approved Sale of such Holder's exercise; and
          (iii) with respect to an Initial Investors Cash-

                                       5
<PAGE>

          Out, if the Holdings Notice states that such event has caused the
          vesting of either of such warrants, the Holder shall notify Holdings
          on or before five days following receipt of the Holdings Notice of
          such Holder's exercise of this Warrant (the "Notice Date") . This
                                                       -----------
          Warrant shall be exercisable by the Holder in whole only, and not in
          part, by the surrender of this Warrant and delivery to Holdings on or
          before the Notice Date of (i) a duly executed notice of exercise in
          the form of Exhibit A (a "Notice of Exercise") and (ii) at the option
                                    ------------------
          of the Holder, either (A) the Exercise Price for the Warrant Shares,
          payable in cash or by wire transfer to a bank account designated by
          Holdings or (B) in the case of a Panthers Merger, a notice by Holder
          to Holdings requesting the Warrant Shares be issued net of the
          appropriate Exercise Price (to be determined based on and consistent
          with the value of the consideration to be tendered in connection with
          such Panthers Merger)."

     (m)  Section 2(g) shall be amended by deleting such section in its entirety
and replacing such section with the following:

          "(g)  This Warrant shall terminate automatically upon the closing of
          an Approved Sale or a Panthers Merger and this Warrant shall no longer
          be of any force or effect, unless (i) provision is made in writing in
          connection with such transaction for the continuance of this Warrant
          and for the assumption of this Warrant, or for the substitution for
          this Warrant of a new Warrant covering the securities of a successor
          entity or an affiliate thereof, with appropriate adjustments as to the
          number and kind of securities and exercise price, in which event this
          Warrant shall continue or be replaced, as the case may be, in the
          manner and under the terms so provided; or (ii) the Board of Directors
          of Holdings shall provide in writing for such adjustment as it deems
          appropriate in terms and conditions of this Warrant, including without
          limitation (A) accelerating the vesting of this Warrant and/or (B)
          providing for the cancellation of this Warrant and its automatic
          conversion into the right to receive the securities, cash or other
          consideration that the Holder would have been entitled to receive upon
          consummation of such Approved Sale or Panthers Merger had Warrant
          Shares been issued and outstanding immediately prior to the Approved
          Sale or Panthers Merger (net of the appropriate exercise price)."

     4.   Notwithstanding anything contained herein to the contrary, in the case
of a Panthers Merger (as defined in Section 3(d) hereof), you may at your
election have the following provisions (a) through (f) become effective upon
your notifying Holdings and IWO of such election in the form set forth as
Exhibit A hereto at any time after the date hereof but in no event later than
ten days following notice provided by Holdings to you and Lowenstein Sandler
P.C. of its request for your determination of such election, provided that such
notice by Holdings shall not be given more than 40 days prior to date of the
meeting of Panthers stockholders to vote in connection with such Panthers Merger
(such meeting date to be determined by the meeting date set forth in the related
proxy statement as of the date of such notice).  Neither any election by

                                       6
<PAGE>

you under this Section 4 nor any other provision of this Section 4 shall be
effective if you have not timely provided such notice or if a Panthers Merger is
not consummated.

     (a) The Employment Agreement shall be terminated upon consummation of such
Panthers Merger and, notwithstanding any other provision thereof to the contrary
and in satisfaction of Holdings' and IWO's obligations thereunder, you shall be
entitled to the rights provided by the first sentence of Section 7(d) thereof
with your bonus compensation for fiscal 2000 being determined as if your
employment had continued through December 31, 2000, but in any case such bonus
compensation for fiscal 2000 shall not be less than 50% of the maximum bonuses
that you would have received under Section 3(b)(i)(A) and (B) of the Employment
Agreement if the goals described therein had been met for fiscal 2000.  In
addition, on the Separation Date (defined below), you shall be entitled to
receive $350,000 as a severance payment.

     (b) For the period from the consummation of such Panthers Merger through a
date (to be determined by the board of directors of Holdings) up to six months
following the consummation of such Panthers Merger (the "Separation Date"), you
will provide all reasonable and necessary assistance to Parent, Holdings and IWO
(as directed by the board of directors of Holdings) in order to ensure the
orderly transition of your duties and responsibilities for Holdings and IWO.
You will be paid for such services a fee equal to six months' of your Base
Compensation (as defined in the Employment Agreement). and will be entitled to
participate in medical, dental and car allowance benefits as if your employment
had continued for six months following such Panthers Merger.  Following such six
month period, you will be entitled to elect to continue medical and dental
coverage in accordance with Section 601 et. seq. of the Employee Retirement
Income Security Act of 1974.  You will also be paid or reimbursed for all
reasonable business travel and other business expenses incurred or paid by you
on or prior to the Separation Date in connection with the performance of your
services upon presentation of expense statements or vouchers and any such other
supporting information as Holdings may request.

     (c) Notwithstanding Section 1 hereof, with respect to the Stock Option
Agreement:

          (i) an Approved Sale shall be deemed to have occurred as of the date
     of the consummation of such Panthers Merger, and all Options which are the
     subject of such agreement shall vest and be exercisable immediately prior
     to the consummation of such Panthers Merger; and

          (ii) subject to Section 6(a) of such agreement, your Options will
     expire on the later of five years after the Termination Date or two years
     after an Initial Public Offering.

     (d) The Warrant shall be further amended as set forth in clauses (i)
through (v) below and shall vest and be exercisable in accordance with the terms
of the Warrant as amended by Section 3 hereof:

          (i) the words "or Termination of Employment" shall be deleted from the
     parenthetical clause in the heading thereof;

                                       7
<PAGE>

          (ii) the words "or in the event of the termination of Holder's
     employment with Holdings or any of its Subsidiaries" shall be deleted from
     the first full paragraph following the heading thereof;

          (iii)  the definitions "Termination of Employment," "Cause,"
     "Disability" and "Retirement" contained in Section 1 thereof shall be
     deleted in their entirety;

          (iv) the words ", provided such occurrence is prior to the Termination
     of Employment" shall be deleted from the first sentence in each of Sections
     2(a) and 2(b) thereof; and

          (v) Section 2(h) shall be deleted in its entirety.

     (e) With respect to the Management Stock Purchase Agreement, Holdings
hereby waives any Repurchase Right (as defined therein) that it may have
pursuant to Section 3(a) thereof and you hereby waive any Put Right (as defined
therein) that you may have pursuant to Section 3(b) thereof.

     (f) You, for yourself, your agents, legal representatives, assigns, heirs,
distributees, devisees, legatees, administrators, personal representatives and
executors ("Your Parties"), on the one hand, and Holdings and IWO, its present,
            ------------
past and future subsidiaries and affiliates, successors and assigns, and their
respective present and past officers, directors, employees and agents ("Our
                                                                        ---
Parties"), on the other hand hereby release and forever discharge the other,
-------
from any and all claims, demands, actions, liabilities and other claims for
relief and remuneration whatsoever, whether known or unknown; provided, however,
that nothing contained herein shall relieve IWO, Holdings or you from any
obligation arising herein, under the agreements referenced herein (as modified
by this agreement), under the Indemnity Agreement dated December 20, 1999
between Holdings and you, under the Indemnity Agreement dated November 5, 1999
between IWO and you, under the Certificate of Incorporation of Holdings or IWO
or under the Stockholders Agreement dated December 20, 1999 between Holdings,
you and the other parties thereto.  Your Parties and Our Parties further agree
not to assert any claim, charge or other legal proceeding against the other, in
any forum, based on any events, whether known or unknown, which are the subject
of the release contained in this Section 4(f).

     5.  Except for the changes described herein, the Stock Option Agreement,
the Warrant, the Management Stock Purchase Agreement and the Employment
Agreement will be unchanged and remain in full force and effect.

     6.  In connection with a Designated Merger if and when requested by the
board of directors of Holdings, you agree to enter into a lockup agreement and a
voting agreement with respect to your shares of capital stock of Holdings and
Parent and any such capital stock that may be acquired upon the exercise of
options or warrants for such capital stock, to the extent and on substantially
the same basis as Investcorp S.A. and its subsidiaries enter into such
agreements with respect to their capital stock of Holdings and Parent.

     7.  You hereby waive any acceleration of benefits pursuant to the Stock
Option Agreement, the Warrant, the Management Bonus Stock Purchase Agreement, or
the Management Stock Purchase Agreement unless shareholder approval meeting the
requirements

                                       8
<PAGE>

of Section 280G(b)(5) of the Internal Revenue Code of 1986, as amended (the
"Code"), with respect to such benefits is obtained.

     8.  You agree that this letter agreement (excluding for this purpose
paragraph 7 of such agreement) shall not be effective unless shareholder
approval meeting the requirements of Section 280G(b)(5) of the Code is obtained.

     9.  This letter agreement shall inure to the benefit of, and be binding
upon, the heirs, executors, administrators, successors and assigns of you,
Holdings and/or IWO.

     8.  The parties hereto agree to take or cause to be taken all such further
actions as may be reasonably necessary or appropriate to effectuate the intent,
purposes and obligations of this letter agreement.

                                       9
<PAGE>

     Please indicate your acceptance of the terms hereof by signing in the
appropriate space below.

                              Very truly yours,


                              IWO HOLDINGS, INC.



                              By: /s/ Steven M. Nielsen
                                  ---------------------
                                  Name: Steven M. Nielsen
                                  Title: Chief Financial Officer



                              INDEPENDENT WIRELESS ONE CORPORATION



                              By: /s/ Steven M. Nielsen
                                  ---------------------
                                  Name: Steven M. Nielsen
                                  Title: Chief Financial Officer

Agreed and accepted:

Solon Kandel


/s/ Solon L. Kandel
--------------------------

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