<PAGE>   1
                                                                    EXHIBIT 10.3

                                                               EXECUTION VERSION

                                SECOND AMENDMENT
                                       TO
                             SECURED LOAN AGREEMENT

            This Second Amendment (the "Second Amendment") to Secured Loan
Agreement is entered into by and between NEXTEL INTERNATIONAL, INC. (the
"Company") and MOTOROLA CREDIT CORPORATION (referred to herein as the "Creditor"
or "MCC").

                              W I T N E S S E T H:

            WHEREAS, the Company has heretofore entered into a Secured Loan
Agreement, dated as of December 16, 1999 with the Creditor and with MCC in its
capacities as collateral agent (in such capacity, the "Collateral Agent") and as
administrative agent (in such capacity, the "Administrative Agent") (as
heretofore amended, modified or supplemented, the "Financing Agreement";
capitalized terms used herein and not otherwise defined herein having the
meanings assigned thereto in the Financing Agreement);

            WHEREAS, the Company has requested that the Creditor agree to
certain amendments to the Financing Agreement; and

            WHEREAS, subject to the terms and conditions set forth herein, the
Creditor is willing to undertake certain amendments to the Financing Agreement.

            NOW, THEREFORE, in consideration of the premises, and intending to
be legally bound hereby, the Company and the Creditor hereby agree as follows:

            SECTION 1.  AMENDMENTS.

            Upon the satisfaction by the Company of the conditions precedent set
forth in Section 2 below, and in reliance on the warranties of the Company set
forth in Section 3 below, the Financing Agreement is hereby amended as follows:

            1.1   Effective as of January 1, 2001, the definition of "Maturity
                  Date" in Section 1.1 of the Financing Agreement is hereby
                  amended and restated in its entirety as follows:

                  " "Maturity Date" means June 30, 2003, provided, if such date
                  is not a Business Day, then the Maturity Date shall be the
                  immediately preceding Business Day."

            1.2   Schedule 1.1(e) to the Financing Agreement is hereby deleted
                  and replaced with Schedule 1.1(e) (Target Cumulative
                  Subscribers) attached hereto.


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            1.3   The term "Borrowing Affiliate" shall be deemed to have the
                  meaning under the Financing Agreement which is given to such
                  term under the MEFA as of the date of this Second Amendment
                  (assuming the effectiveness of the Fourth Amendment thereto).

            1.4   Clauses (a), (b) and (c) of Section 7.15 of the Financing
                  Agreement are hereby amended and restated in their entirety as
                  follows:

                  "(a) a ratio of Indebtedness to EBITDA of not greater than the
            ratios set forth below, measured at the end of each fiscal quarter
            of the Company commencing with the fiscal quarter ending September
            30, 2002:

<TABLE>
<CAPTION>
              Quarter end date             Maximum Indebtedness to EBITDA
<S>                                       <C>
              9/30/02                      169.6: 1
              12/31/02                     51.0 : 1
              3/31/03                      27.0 : 1
</TABLE>

                  (b) The product of (i) four times (ii) EBITDA, measured for
            the most recently ended fiscal quarter commencing with the fiscal
            quarter ending December 31, 2000, of not less than the amount on the
            quarter end dates set forth below:

<TABLE>
<CAPTION>
              Quarter end date           Minimum EBITDA
              ----------------           --------------
<S>                                      <C>
              12/31/00                   (207,000,000)
              3/31/01                    (176,000,000)
              6/30/01                    (176,000,000)
              9/30/01                    (102,000,000)
              12/31/01                    (60,000,000)
              3/31/02                     (31,000,000)
              6/30/02                      (8,000,000)
              9/30/02                      17,000,000
              12/31/02                     56,000,000
              3/31/03                     105,000,000
</TABLE>

                  (c) Notwithstanding anything herein to the contrary
            (including, without limitation, the provisions of Section 10.1
            hereof), a breach of Section 7.15(a) or Section 7.15(b) hereof as of
            any quarter end date shall not constitute an


                                      -2-
<PAGE>   3
            Event of Default hereunder unless the Aggregate Subscribers as of
            the end of such quarter were less than the "Total Ending
            Consolidated Digital Subscribers" set forth opposite the quarter end
            dates set forth in Schedule 1.1(e)."

            SECTION 2.  CONDITIONS.

            As conditions precedent to the effectiveness of the Second
Amendment, each of the following shall have occurred:

             2.1 the Company shall have delivered to the Creditor the Second
       Amendment, duly executed and delivered and appropriately dated and in
       form and substance satisfactory to the Creditor;

            2.2 the Creditor shall have received an opinion of counsel for the
      Company with respect to this amendment, reasonably acceptable to the
      Creditor, and shall, within 30 days of the date hereof, receive an opinion
      of Canadian counsel to the Company with respect to the collateral in
      respect of the obligations of the Company under the Financing Agreement,
      as amended by this amendment;

             2.3 the Creditor shall have received within 10 Business Days of the
       date hereof a binding commitment, reasonably acceptable to the Creditor,
       with respect to the purchase by the Company and its affiliates of minimum
       amounts of goods and services from the Creditor or its affiliates;

             2.4 all necessary consents to the Second Amendment have been
       obtained from third parties, including assignees of the Creditor and
       insurers of the payment of Advances; and

            2.5 the Company shall have delivered such other documents as the
      Creditor may reasonably request;

      it being understood and agreed that the failure to satisfy either of the
      conditions in paragraphs 2.2 and 2.3 above in the time periods specified
      shall result in the Second Amendment being void ab initio and of no force
      and effect.


            SECTION 3. REPRESENTATIONS AND WARRANTIES.

      To induce the Creditor to enter into the Second Amendment, the Company
hereby represents and warrants to the Creditor as of the date hereof (and shall
be deemed to represent and warrant as of the initial date of effectiveness of
this Second Amendment) that:

            3.1 The representations and warranties contained in the Financing
      Agreement and the other Credit Documents are true and correct in all
      material respects on and as of the


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<PAGE>   4
      date hereof, except for representations and warranties that speak as of a
      particular date, in which case such representations and warranties are
      true as of such date;

            3.2 There has been no Material Adverse Effect since September 30,
      2000;

            3.3 The consolidated audited balance sheets of the Company and its
      Subsidiaries and consolidated statements of operations, changes in
      stockholders' equity and cash flows of the Company and its Subsidiaries
      each as of December 31, 1999, and all other information and data
      heretofore furnished by the Company, or any agent of the Company on behalf
      of the Company to the Creditor, including, the quarterly (each as at
      September 30, 2000) consolidated balance sheets and consolidated
      statements of operations, changes in stockholders' equity and cash flows,
      have been prepared in accordance with GAAP and fairly present the
      condition and results of operations of the Company and its Subsidiaries as
      of such dates or for such periods;

            3.4 Each Credit Party has made all material required contributions
      under the Plans for all periods through and September 30, 2000, or
      adequate accruals therefor have been provided for in the financial
      statements referenced in paragraph 3.3 above;

            3.5 The actuarial value of vested benefits required to be funded by
      each Credit Party, or with respect to which such Credit Party is liable,
      under the Plans, determined using the actuarial methods and assumptions
      used by the relevant Plan's actuary as of the last valuation date for
      which an actuarial valuation was completed to determine such Plan's funded
      status, did not as of the last valuation date as of which an actuarial
      valuation has been completed, which in the case of any individual Plan was
      not earlier than January 1, 2000, exceed the actuarial value of the assets
      of the Plans allocable to such vested and non-vested benefits by a
      material amount; and

            3.6 After giving effect to the Second Amendment, no Default or Event
      of Default has occurred and is continuing and all of the guarantees and
      Security Documents shall be in full force and effect with the same
      priority (and with no need for any additional agreements, instruments or
      filings to preserve the effectiveness or priority) as in effect
      immediately prior to the Second Amendment.

            SECTION 4. GENERAL.

                  4.1 Reservation of Rights. The Company acknowledges and agrees
            that the execution and delivery of the Second Amendment shall not be
            deemed (i) to create a course of dealing or otherwise obligate the
            Creditor to forbear or execute similar amendments under the same or
            similar circumstances in the future, or (ii) as a waiver by the
            Creditor of any covenant, condition, term or provision of the
            Financing Agreement or any of the other Credit Documents, and the
            failure of the Creditor to require strict performance by the Company
            or any other Credit Party of any provision thereof shall not waive,
            affect or diminish any right of the Creditor to thereafter demand
            strict compliance therewith. The Creditor hereby reserves all


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<PAGE>   5
            rights granted under the Financing Agreement, the other Credit
            Documents and the Second Amendment.

            4.2 Full Force and Effect. As hereby modified, the Financing
            Agreement and each of the other Credit Documents shall remain in
            full force and effect and each is hereby ratified, approved and
            confirmed in all respects.

            4.3 Affirmation. The Company hereby affirms its obligations under
            Section 4 of the Financing Agreement and agrees to pay on demand all
            reasonable costs and expenses of the Creditor in connection with the
            preparation, execution and delivery of the Second Amendment and all
            instruments and documents delivered in connection herewith.

            4.4 Successors and Assigns. The Second Amendment shall be binding
            upon and shall inure to the benefit of the Company, the Creditor and
            the respective successors and assigns of the Company and the
            Creditor.

            4.5 Counterparts. The Second Amendment may be executed in any number
            of counterparts and by the different parties on separate
            counterparts, and each such counterpart shall be deemed to be an
            original, but all such counterparts shall together constitute but
            one and the same Second Amendment.

                                    * * * * *


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<PAGE>   6
      IN WITNESS WHEREOF, the Company and the Creditor have executed this Second
Amendment as of the 19th day of February, 2001.



                                    COMPANY:


                                    NEXTEL INTERNATIONAL, INC.

                                    By: /s/ Robert J. Gilker
                                        ---------------------------------
                                    Name  Robert J. Gilker
                                          -------------------------------
                                    Title: Vice President & General Counsel
                                          -------------------------------

                                    CREDITOR:

                                    MOTOROLA CREDIT CORPORATION


                                    By:   /s/ Gary B. Tatje
                                        ---------------------------------
                                    Name:     Gary B. Tatje
                                          -------------------------------
                                    Title:    Vice President
                                          -------------------------------


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<PAGE>   7
                                 Schedule 1.1(e)


<TABLE>
<CAPTION>
                  TOTAL ENDING
                   CONSOLIDATED
                DIGITAL SUBSCRIBERS
<S>             <C>
4Q00                  538,496
1Q01                  632,146
2Q01                  720,267
3Q01                  814,645
4Q01                  915,566
1Q02                1,022,001
2Q02                1,134,497
3Q02                1,252,623
4Q02                1,374,215
1Q03                1,492,409
</TABLE>


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