<PAGE>
                                                                   Exhibit 10.55

PORTIONS OF THIS EXHIBIT WERE OMITTED AND HAVE BEEN FILED SEPARATELY WITH THE
SECRETARY OF THE COMMISSION PURSUANT TO THE COMPANY'S APPLICATION REQUESTING
CONFIDENTIAL TREATMENT UNDER RULE 24B-2 OF THE SECURITIES EXCHANGE ACT.

                                               Mexico City, December 13th, 2002.

AOL MEXICO, S. DE R.L. DE C.V.
Blvd. Manuel Avila Camacho 36_5(degree) Piso
Col. Lomas de Chapultepec
Mexico, 11000, D.F.

                       ATT'N: Lic. Fernando Zetina Arbesu.

According to section 10 of the Master Agreement for Data Communications and
Value Added Services, dated January 20, 2000 (hereinafter referred to as the
"MAIN AGREEMENT"), AVANTEL shall destine a [**]% of invoiced amount less taxes
to joint marketing efforts or, at AOL's option, promotions of AVANTEL's
communications services through the service provided under the MAIN AGREEMENT to
AOL's subscribers. Under the MAIN AGREEMENT, AVANTEL, S.A. (hereinafter referred
to as the "AVANTEL") provides AOL MEXICO, S. DE R.L. DE C.V. (hereinafter
referred to as the "AOL") port installation, activation, maintenance and
operation services for AOL Switched Access National Network.

Both AVANTEL and AOL has reached the following agreements:

         (i)      During a period that goes from July 11, 2000, to December 31,
                  2002, AVANTEL acknowledges that it has received from AOL
                  payments under the MAIN AGREEMENT in the amount of MXP$[**]
                  (currency of the United Mexican States), as detailed in Annex
                  1.

         (ii)     According to Section 10 of the MAIN AGREEMENT, the [**]% of
                  the invoiced amount less taxes is equal to MXP$[**] (currency
                  of the United Mexican States).

                  (a)      AVANTEL shall destine the abovementioned amount in
                           the amounts, time and manner detailed as follows:

                           o        AVANTEL will buy advertising from AOL in the
                                    amount of USD$[**] (United States Dollars)
                                    in calendar year 2003, and USD$[**] (United
                                    States Dollars) in calendar year 2004. Such
                                    amounts will be paid by AVANTEL on monthly
                                    basis each one in the amount of USD$[**]
                                    (United States Dollars) beginning on January
                                    2003 and ending on December 2004.

                           o        The balance of the [**]% (MXP$[**])
                                    accumulated from July 2000 until December
                                    2002, will be included as a discount in
                                    AVANTEL's monthly invoices for dedicated
                                    ports rendered under the MAIN AGREEMENT.
                                    SUCH DISCOUNTS SHALL BE MADE ON A MONTHLY

<PAGE>

                                    BASIS BETWEEN January 2003 to December 2004
                                    in the amount of MXP$[**] (currency of the
                                    United Mexican States).

         (iii)    In addition, for calendar years 2003 and 2004 the obligation
                  AVANTEL assumed under section 10 of the MAIN AGREEMENT will be
                  fulfilled as follows:

                  (a)      AVANTEL and AOL agreed on December 2002 a forecast of
                           the service under the MAIN AGREEMENT that shall be
                           invoiced by AVANTEL to AOL. Such amount is up to
                           approximately MXP$[**] (currency of the United
                           Mexican States).

                  (b)      After applying the [**]% mentioned on section 10 of
                           the MAIN AGREEMENT, the result is equal to MXP$[**]
                           (currency of the United Mexican States); this amount
                           will be divided by 12, and the monthly applicable
                           discount to be made by AVANTEL from January to
                           November 2003 will be for MXP$[**] (currency of the
                           United Mexican States). The discount set forth in the
                           Section (iii)(b) shall be in addition to the discount
                           provided for under Section (ii)(a) above.

                  (c)      On November 2003, AVANTEL and AOL will revise the
                           projected monthly discounts against the real
                           discounts that should have been done during the
                           preceeding months, and a final adjustment will be
                           made on December 2003.

                  (d)      The same procedure will be done for the year 2004,
                           and the corresponding discounts shall be in addition
                           to the discounts provided for under Section (ii)(a)
                           above..

In case AVANTEL does not include the discount in the AOL invoices issued during
2003 and 2004 under sections (ii) and (iii) of this letter agreement, AVANTEL
expressly authorizes AOL to subsctract the amount of the corresponding discount
directly for the corresponded invoice; this action will not be considered as a
breach of the payment obligations AOL has under the provisions of the MAIN
AGREEMENT.

Except as expressly provided herein, nothing in this letter agreement shall be
deemed to waive or modify any of the provisions of the MAIN AGREEMENT, or any
amendment or addendum thereto. Except as provided in this letter agreement and
in the port cancellation letter agreement of the same date, all other terms and
conditions of the MAIN AGREEMENT shall remain in full force and effect, and the
parties hereto acknowledge that such terms and conditions are in full force and
effect as of the date hereof. This letter agreement may be executed in Spanish
and English, provided however that the Spanish version shall always prevail in
the event of any disputes concerning this letter agreement.

                                       2
<PAGE>


If you agree on the terms and conditions of this letter agreement, please sign
one original of this document for your records and return the other original to
AVANTEL

Very truly yours,

         AVANTEL, S.A



         /S/ FERNANDO BELLIDO CASTANOS
---------------------------------------------
         MR. FERNANDO BELLIDO CASTANOS

ACCEPT AND AGREED:



DATE:     DECEMBER 13, 2002
     ----------------------------------------
         AOL MEXICO, S. DE R.L. DE C.V.


          /S/ FERNANDO ZETINA ARBESU
     ----------------------------------------
         LIC. FERNANDO ZETINA ARBESU


                                       3

<PAGE>
                                     ANNEX 1


AOL MEXICO
OPERATION SUMMARY WITH AVANTEL
(INVOICES PAID UNTIL DECEMBER 31, 2002)

<TABLE>
<CAPTION>
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
SHARED PORTS
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
        INVOICE                PERIOD                          AMOUNT                VAT                 TOTAL
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
<S>                        <C>              <C>          <C>                  <C>                 <C>
27660                     Jun-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
29117                     Jul-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
30558                     Aug-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
32629                     Sep-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
35030                     Oct-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
36626                     Nov-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
37899                     Dec-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
40175                     Jan-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
41510                     Feb-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
42843                     Mar-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
43636                     Apr-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
44708                     May-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
46407                     Jun-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
47929                     Jul-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
49295                     Aug-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
73887                     Sep-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
73887                     Oct-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
73887                     Nov-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
73887                     Dec-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
Subtotal                                                 [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
DEDICATED PORTS                                          [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jul-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Aug-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Sep-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Oct-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Nov-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Dec-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jan-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Feb-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Mar-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Mar-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Apr-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      May-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jun-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jul-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Aug-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Sep-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
</TABLE>
<PAGE>

<TABLE>
<CAPTION>

------------------------- ----------------- ------------ -------------------- ------------------- --------------------
SHARED PORTS
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
        INVOICE                PERIOD                          AMOUNT                VAT                 TOTAL
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
<S>                        <C>              <C>          <C>                  <C>                 <C>
[**]                      Oct-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Oct-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Nov-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Dec-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jan-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Feb-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Mar-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Apr-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      May-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jun-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jul-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Aug-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Sep-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Oct-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Nov-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Dec-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                                                     [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                                                     [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jul-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Aug-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Sep-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Oct-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Nov-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Dec-00                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jan-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Feb-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Mar-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Apr-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      May-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jun-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jul-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Aug-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Sep-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Oct-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Nov-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Dec-01                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jan-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Feb-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Mar-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Apr-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      May-02                         [**]                 [**]                [**]
------------------------ ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jun-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Jul-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
</TABLE>
<PAGE>
<TABLE>
<CAPTION>
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
SHARED PORTS
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
        INVOICE                PERIOD                          AMOUNT                VAT                 TOTAL
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
<S>                        <C>              <C>          <C>                  <C>                 <C>
[**]                      Aug-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Sep-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Oct-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Nov-02                         [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
[**]                      Dec-02                         [**]                 [**]                [**]
------------------------ ----------------- ------------ -------------------- ------------------- --------------------
Subtotal                                                 [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
Total                                                    [**]                 [**]                [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
                      5%                                 [**]                 [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
IM Buy 2003-2004                                         [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
                                                         [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
Monthly Credit 2003-2004                                 [**]
------------------------- ----------------- ------------ -------------------- ------------------- --------------------
</TABLE>