TRESCOM INTERNATIONAL INC
SC 13D/A, 1998-04-24
TELEGRAPH & OTHER MESSAGE COMMUNICATIONS
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<PAGE>
 
                                 UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549

                                 SCHEDULE 13D
                                (Rule 13d-101)

    INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO 13d-1(a) AND
                 AMENDMENTS THERETO FILED PURSUANT TO 13d-2(a)
                           (Amendment No. 1)/1/

                          TresCom International, Inc.
________________________________________________________________________________
                               (Name of Issuer)


                   Common Stock, par value $.0419 per share
________________________________________________________________________________
                        (Title of Class of Securities)

                                  895307 10 6

________________________________________________________________________________
                                (CUSIP Number)

                 Primus Telecommunications Group, Incorporated
                              1700 Old Meadow Rd.
                               McLean, VA 22102
                                (703) 902-2800

________________________________________________________________________________
                 (Name, Address and Telephone Number of Person
               Authorized to Receive Notices and Communications)


                                April 16, 1998

________________________________________________________________________________
            (Date of Event which Requires Filing of this Statement)


If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box [_].


Note:  Six copies of this statement, including all exhibits, should be filed
with the commission.  See Rule 13d-1(a) for other parties to whom copies are to
be sent.

__________
(1)  The remainder of this cover page shall be filled out for a reporting
     person's initial filing on this form with respect to the subject class of
     securities, and for any subsequent amendment containing information which
     would alter disclosures provided in a prior cover page.

     The information required on the remainder of this cover page shall not be
     deemed to be "filed" for the purpose of Section 18 of the Securities
     Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of
     that section of the Act but shall be subject to all other provisions of the
     Act (however, see the Notes).

                               Page 1 of 6 Pages
<PAGE>
 
                                 SCHEDULE 31D

- -----------------------                                  ---------------------
  CUSIP NO. 895307 10 6                                    PAGE 2 OF 6 PAGES
- -----------------------                                  ---------------------
 
- ------------------------------------------------------------------------------
 1    NAME OF REPORTING PERSON
      S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
                          
      Primus Telecommunications Group, Incorporated
- ------------------------------------------------------------------------------
 2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                (a) [_]
                                                                (b) [_]
- ------------------------------------------------------------------------------
 3    SEC USE ONLY
  
 
- ------------------------------------------------------------------------------
 4    SOURCE OF FUNDS*  OO
      
      
- ------------------------------------------------------------------------------
 5    CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT 
      TO ITEMS 2(d) or 2(e)                                         [_]
       
- ------------------------------------------------------------------------------
 6    CITIZENSHIP OR PLACE OF ORGANIZATION
      
      State of Delaware  
- ------------------------------------------------------------------------------
                     7    SOLE VOTING POWER
                           
     NUMBER OF            
                          6,570,095 Shares   
      SHARES       -----------------------------------------------------------
                     8    SHARED VOTING POWER
   BENEFICIALLY           
                          
     OWNED BY             N/A       
                   -----------------------------------------------------------
       EACH          9    SOLE DISPOSITIVE POWER
                           
    REPORTING             
                          N/A
      PERSON       -----------------------------------------------------------
                     10   SHARED DISPOSITIVE POWER
       WITH               
                          N/A       
- ------------------------------------------------------------------------------
 11   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
      
      
      6,570,095 Shares
- ------------------------------------------------------------------------------
 12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*
                    
      [_]
- ------------------------------------------------------------------------------
 13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
      
      54.2%            
- ------------------------------------------------------------------------------
 14   TYPE OF REPORTING PERSON*
  
      CO
- ------------------------------------------------------------------------------

                               Page 2 of 6 Pages
<PAGE>
 
                            SCHEDULE 13D STATEMENT
                            ----------------------

ITEM 1    SECURITY AND ISSUER:
          --------------------

               This Amendment No. 1 amends and supplements the statement on
Schedule 13D, dated March 12, 1998 (the "Original Schedule"), (as amended, the
"Schedule 13D"), of Primus Telecommunications Group, Incorporated ("Primus"),
with respect to shares of Common Stock (the "Common Stock"), par value $.0419
per share, of TresCom International, Inc. (the "Issuer") as follows:

ITEM 3.   SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.
          --------------------------------------------------

               Item 3 is amended to report that, in addition to that set forth 
in the Original Schedule, as of April 16, 1998, Primus, Taurus Acquisition
Corporation, a Florida corporation and a wholly-owned subsidiary of Primus
("TAC"), and the Issuer, entered into Amendment No. 2 to Agreement and Plan of
Merger (the "Amendment"), dated as of February 3, 1998, by and among Primus, TAC
and the Issuer, and as amended by Amendment No. 1 to Agreement and Plan of
Merger, dated as of April 8, 1998, by and among Primus, TAC and the Issuer (as
amended, the "Merger Agreement"). In connection with the Amendment, as of April
16, 1998, Warburg, Pincus Investors, L.P. ("Warburg, Pincus") agreed to amend
the stockholder agreement by and among Primus, TAC, K. Paul Singh and Warburg,
Pincus, dated as of February 3, 1998 (the "Amendment to the Stockholder
Agreement"). Also in connection with the Amendment, as of April 16 1998, Messrs.
Wesley T. O'Brien and Rudolph McGlashan agreed to amend their voting agreements
between each of them on the one hand, and Primus on the other hand, dated as of
February 3, 1998 (the "Amendment to the Issuer Voting Agreements", collectively
with the Amendment to the Stockholder Agreement, the "Amendments to the Issuer
Shareholder Agreements").

                               Page 3 of 6 Pages
<PAGE>
 
ITEM 4.        PURPOSE OF TRANSACTION.
               -----------------------

               Item 4 is amended to report that, in addition to that set forth 
in the Original Schedule, the purpose of the Amendments to the Issuer
Shareholder Agreements was to provide Primus with additional inducement to
effect the merger.

ITEM 5         INTEREST IN SECURITIES OF THE ISSUER
               ------------------------------------
 
               Item 5 is amended to report:

     (A)  As of April 16, 1998, Primus beneficially owns 6,813,408 shares or
approximately 52.78% of the outstanding Common Stock.

     (B)  Primus has the sole power to vote the shares.

     (C)  Not applicable.

                               Page 4 of 6 Pages
<PAGE>
 
     (D)  Not applicable.

     (E)  Not applicable.

ITEM 6.   CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR 
          RELATIONSHIPS WITH RESPECT TO SECURITIES OF THE ISSUER.
          ------------------------------------------------------

          Item 6 is amended to report that pursuant to the Amendments to the
Issuer Shareholder Agreements, Warburg, Pincus, and Messrs. O'Brien and
McGlashan agreed to grant Primus options to purchase their shares of Issuer
common stock at an exercise price per share of $12.00 (based on the volume-
weighted average sales price per share of Primus common stock for the 20 
trading-day period ending on the third trading day prior to the exercise of the
option), payable in shares of Primus common stock, if the Merger Agreement
terminates under defined circumstances. The defined circumstances under which
the options may be exercised by Primus are those in which the Merger Agreement
would be terminated by either Primus or the Issuer and Primus would be entitled
to the termination fee as provided for in the Merger Agreement. Additionally,
pursuant to the Amendment to the Stockholder Agreement, if the option granted by
Warburg, Pincus is exercised, Warburg, Pincus has agreed to use its reasonable
best efforts to cause the existing Warburg, Pincus designees to the Issuer board
of directors to resign, and upon such resignations, Issuer has agreed to use its
reasonable best efforts to restructure the Issuer board of directors so that
designees of Primus constitute a majority of the members of the Issuer board of
directors. Primus also agreed, if it exercises the option granted by Warburg,
Pincus, to offer to acquire all outstanding shares of Issuer common stock not
otherwise owned by Primus or its affiliates, at the same price paid to Warburg,
Pincus, and payable in shares of Primus common stock. The termination provisions
of the Amendments to the Issuer Shareholder Agreements were also amended to
provide for the survival of the irrevocable proxy so long as the options are
exercisable, and for the survival of the option beyond the termination of the
Issuer Shareholder Agreements.

          The foregoing summary of the Amendment and the Amendments to the
Issuer Shareholder Agreements is qualified in its entirety by reference to the
amendments which are filed as exhibits to this Schedule 13D reference to which
is hereby made for the full text thereof.

ITEM 7.        MATERIAL TO BE FILED AS EXHIBITS.
               -------------------------------- 

          1.   Amendment No. 2 to Agreement and Plan of Merger by and among 
               Primus, TAC, and the Issuer, dated as of April 16, 1998.

<PAGE>
 
          2.   Amendment No. 1 to Stockholder Agreement by and among Primus,
               TAC, K. Paul Singh, Warburg, Pincus and the Issuer dated as of
               April 16, 1998.

          3.   Amendment No. 1 to Voting Agreement by and between Primus and
               Wesley T. O'Brien, dated as of April 16, 1998.

          4.   Amendment No. 1 to Voting Agreement by and between Primus and
               Rudolph McGlashan, dated as of April 16, 1998.

SIGNATURE

     After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.



                              PRIMUS TELECOMMUNICATIONS GROUP, INCORPORATED


                         
April 23, 1998      By:  /s/ Neil L. Hazard
                         ---------------------------------
                              Neil L. Hazard,
                              Executive Vice President

                               Page 6 of 6 Pages
<PAGE>

Schedule A is amended and restated as follows:
 
                                  SCHEDULE A
                                  ----------

<TABLE>
<CAPTION>
- ------------------------------------------------------------------------------ 
NAME                    CITIZEN-SHIP  POSITION WITH           PRESENT
                                      PRIMUS                  PRINCIPAL
                                                              OCCUPATION
- ------------------------------------------------------------------------------
<S>                     <C>           <C>                     <C>              
K. Paul Singh           United        Chairman of             President of
c/o Primus              States of     the Board,              Primus
Telecommunications      America       Chief                   
Group, Inc.                           Executive               
1700 Old Meadow Rd.                   Officer and             
McLean, VA 22102                      President               
- ------------------------------------------------------------------------------ 
Neil L Hazard           United        Executive               Chief
c/o Primus              States of     Vice                    Financial
Telecommunications      America       President and           Officer of
Group, Inc.                           Chief                   Primus
1700 Old Meadow Rd.                   Financial               
McLean, VA 22102                      Officer                 
- ------------------------------------------------------------------------------ 
John F. DePodesta       United        Executive               Executive Vice
c/o Primus              States of     Vice                    President of
Telecommunications      America       President --            Primus
Group, Inc.                           Law and                 
1700 Old Meadow Rd.                   Regulatory              
McLean, VA 22102                      Affairs and             
                                      Director                
- ------------------------------------------------------------------------------ 
John Melick             United        Vice                    Vice President
c/o Primus              States of     President of            of Primus
Telecommunications      America       International           
Group, Inc.                           Business                
1700 Old Meadow Rd.                   Development             
McLean, VA 22102                                              
- ------------------------------------------------------------------------------ 
Ravi Bhatia             Australia     Chief                   Chief
c/o Primus                            Operating               Operating
Telecommunications                    Officer of              Officer of
Pty, Ltd.                             Primus                  Primus
55 King Street                        Telecommunica           Australia,
Melbourne, Victoria,                  tions Pty,              c/o Primus
Australia                             Ltd., a                 Telecommunicat 
                                      wholly owned            ions Pty, Ltd. 
                                      subsidiary of           55 King Street 
                                      Primus                  Melbourne,     
                                                              Victoria,      
                                                              Australia       
- ------------------------------------------------------------------------------ 
</TABLE> 
<PAGE>
 
<TABLE> 
<CAPTION> 
- ------------------------------------------------------------------------------
NAME                    CITIZEN-SHIP  POSITION WITH           PRESENT
                                      PRIMUS                  PRINCIPAL
                                                              OCCUPATION
- ------------------------------------------------------------------------------
<S>                     <C>           <C>                     <C>              
Yousef Javadi           United        Chief                   President and
c/o Primus              States of     Operating               Chief
Telecommunications      America       Officer of              Operating
Group, Inc.                           Primus                  Officer of
1700 Old Meadow Rd.                   Telecommunica           Primus
McLean, VA 22102                      tions, Inc.,            Telecommunicat 
                                      a wholly                ions, Inc. 
                                      owned                   1700 Old  
                                      subsidiary of           Meadow Rd.
                                      Primus                  McLean, VA
                                                              22102      
- ------------------------------------------------------------------------------ 
Herman Fialkov          United        Director                Consultant to   
c/o Primus              States of                             Newlight        
Telecommunications      America                               Management LLC  
Group, Inc.                                                   500 North Broadway
1700 Old Meadow Rd.                                           Suite 144  
McLean, VA 22102                                              Jericho, NY 11753 
- ------------------------------------------------------------------------------ 
David E. Hershberg      United        Director                President and    
c/o Primus              States of                             Chief Executive  
Telecommunications      America                               Officer of       
Group, Inc.                                                   Globecomm Systems,
1700 Old Meadow Rd.                                           Inc., 45 Oser Ave.
McLean, VA 22102                                              Hauppaugge, NY   
                                                              11788             
- ------------------------------------------------------------------------------ 
John Puente             United        Director                Chairman of 
c/o Primus              States of                             Telogy Networks,
Telecommunications      America                               Inc., 20250
Group, Inc.                                                   Century Blvd.
1700 Old Meadow Rd.                                           Germantown, MD
                                                              20874
McLean, VA 22102
- ------------------------------------------------------------------------------ 
</TABLE>









<PAGE>
 
                                                                   EXHIBIT 99.E
                                                                   ------------


                AMENDMENT NO. 2 TO AGREEMENT AND PLAN OF MERGER
                -----------------------------------------------

     This Amendment No. 2 to Agreement and Plan of Merger (this "Amendment No.
2") is made and entered into as of April 16, 1998, by and among Primus
Telecommunications Group, Incorporated, a Delaware corporation (the
"Purchaser"), Taurus Acquisition Corporation, a Florida corporation and wholly-
owned subsidiary of the Purchaser (the "Purchaser Subsidiary"), and TresCom
International, Inc., a Florida corporation (the "Target").  The Purchaser, the
Purchaser Subsidiary and the Target are referred to collectively herein as the
"Parties."

                              W I T N E S S E T H:
                              - - - - - - - - - - 

     WHEREAS, the Purchaser, the Purchaser Subsidiary and the Target previously
entered into an Agreement and Plan of Merger dated as of February 3, 1998 (the
"Original Agreement") and an Amendment No. 1 to Agreement and Plan of Merger
dated as of April 8, 1998 (the "Amendment No. 1", and together with the Original
Agreement, the "Amended Agreement");

     WHEREAS, concurrently with this Amendment No. 2, and as a condition hereto,
the Parties, Mr. K. Paul Singh, and the Stockholder are entering into an
amendment to the Stockholder Agreement; and

     WHEREAS, it is now the intention of the Parties to amend the Amended
Agreement as set forth below;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
and agreements contained herein, and for other good and valuable consideration,
the receipt and sufficiency of which is hereby acknowledged, the Parties agree
as follows:

     1.   The definition of "Purchaser-owned Share" contained in Section 1 of 
the Original Agreement is hereby amended and restated in its entirety as 
follows:

     "'Purchaser-owned Share' means any Target Share that is beneficially owned 
       ---------------------
by any Purchaser Company, except for any Target Shares beneficially owned by any
Purchaser Company due to any provisions contained in (i) the Stockholder 
Agreement, dated as of February 3, 1998, and as subsequently amended as of April
16, 1998, by and among Stockholder, Purchaser, Purchaser Subsidiary, K. Paul 
Singh and Target; and (ii) the Voting Agreements, dated as of February 3, 1998, 
and as subsequently amended as of April 16, 1998, by and between Messrs. Wesley 
T. O'Brien and Rudolph McGlashan, on the one hand, and Purchaser, on the other 
hand."

     2.   Section 2(d)(v) of the Amended Agreement is hereby amended and
restated in its entirety as follows:

          "(v)  Conversion of Target Shares.  At and as of the Effective Time,
                ---------------------------                                   
     (A) each issued and outstanding Target Share (other than any Purchaser-
     owned Shares) shall be converted into the right to receive the Per Share
     Merger Consideration, and all such Target Shares shall no longer be
     outstanding, shall be canceled and retired, shall cease to exist, and each
     holder of a certificate representing any such Target Shares shall
     thereafter cease to have any rights with respect to such Target Shares,
     except the right to receive the Per Share Merger Consideration for such
     Target Shares upon the surrender of such certificate in accordance with
     (S)2(e) below, and (B) each Purchaser-owned Share and each Target Share
     held in the treasury of the Target or by any Subsidiary of the Target shall
     be canceled without payment therefor; provided, however, that the Per Share
                                           -----------------                    
     Merger Consideration shall be subject to proportionate adjustment in the
     event of any stock split, stock dividend or reverse stock split.  No Target
     Share shall be deemed to be outstanding or to have any rights other than
     those set forth above in this (S)2(d)(v) after the Effective Time.  As used
     herein, the term "Per Share Merger Consideration" shall mean that number of
                       ------------------------------                           
     Purchaser Shares determined by applying to each Target Share an
<PAGE>

     exchange ratio (the "Exchange Ratio") determined as follows:  the Exchange
                          --------------                                       
     Ratio shall be the quotient of $12.00 divided by the Weighted Average Sales
     Price of a Purchaser Share as of the Closing Date.  Notwithstanding
     anything in this (S)2(d)(v), no fractional Purchaser Shares shall be issued
     to holders of Target Shares.  In lieu thereof, each holder of shares of
     Target Shares who would otherwise have been entitled to receive a fraction
     of a Purchaser Share (after taking into account all certificates delivered
     by such holder at any one time) shall receive an amount in cash equal to
     such fraction of a Purchaser Share, multiplied by the Weighted Average
     Sales Price of a Purchaser Share as of the Closing Date.  "Weighted Average
                                                                ----------------
     Sales Price of a Purchaser Share" means the volume-weighted average sales
     --------------------------------                                         
     price per Purchaser Share as reported by Bloomberg Information Systems,
     Inc. during a period consisting of the third Nasdaq trading day prior to
     the date as of which the Weighted Average Sales Price of a Purchaser Share
     is being determined and the nineteen (19) consecutive trading days prior to
     such day (the "Valuation Period")."
                    ----------------    

     3.   Section 3(h) of the Amended Agreement is hereby amended and restated
in its entirety as follows:

          "(h)  Compliance.  Except as set forth in (S)3(h) of the Target
                ----------                                               
     Disclosure Letter, the Target and its Subsidiaries are in compliance with
     all applicable foreign, federal, state and local laws, rules and
     regulations except where the failure to be in compliance could not
     reasonably be expected to have a material adverse effect on the business,
     financial condition or results of operations of the Target and its
     Subsidiaries taken as a whole."

     4.   Section 3(l) of the Amended Agreement is hereby amended and restated
in its entirety as follows:

          "(l)  Fairness Opinion.  (i)  The Robinson-Humphrey Company, LLC has
                ----------------                                              
     delivered to the Target Board the Target Fairness Opinion, and a true and
     complete copy thereof has been furnished to the Purchaser.  (ii) The
     Robinson-Humphrey Company, LLC has not withdrawn the Target Fairness
     Opinion."

     5.   Section 3(n) of the Amended Agreement is hereby amended and restated
in its entirety as follows:

          "(n)  Florida Business Corporation Law.  For purposes of Section
                --------------------------------                          
     607.0902 of the Florida Business Corporation Law, the execution and
     delivery of the Stockholder Agreement, and the purchase of Target Shares or
     other securities issued by the Target by Purchaser Companies, including
     pursuant to the Stockholder Agreement and the voting agreements referred to
     in the preambles of this Agreement, will not constitute a "control share
     acquisition" as defined in Section 607.0902(2) of the Florida Business
     Corporation Law."

     6.   Section 4(j) of the Amended Agreement is hereby amended and restated
in its entirety as follows:

                                      -2-
<PAGE>
 
          "(j)  Fairness Opinion.  (i)  BT Alex. Brown Incorporated has
                ----------------                                       
     delivered to the Purchaser Board the Purchaser Fairness Opinion, and a true
     and complete copy thereof has been furnished to the Target.  (ii) BT Alex.
     Brown Incorporated has not withdrawn the Purchaser Fairness Opinion."

     7.   Section 4(l) of the Amended Agreement is hereby amended and restated
in its entirety as follows:

          "(l)  Compliance.  The Purchaser and its Subsidiaries are in
                ----------                                            
     compliance with all applicable foreign, federal, state and local laws,
     rules and regulations except where the failure to be in compliance could
     not reasonably be expected to have a material adverse effect on the
     business, financial condition or results of operations of the Purchaser and
     its Subsidiaries taken as a whole."

     8.   Section 5(d)(iv) of the Amended Agreement is hereby amended and
restated in its entirety as follows:

          "(iv)  after April 16, 1998 and prior to May 31, 1998, without first
     having consulted with the Purchaser, none of the Target or its Subsidiaries
     will enter into any legally binding written commitment or obligation with
     respect to, or incur any indebtedness for borrowed money with respect to,
     (1) any capitalized lease, (2) any capital expenditure, including equipment
     purchases, (3) any fees, costs or expenses relating to the transactions
     contemplated hereby, (4) any acquisition earn-out payments or (5) any
     compensation (including, without limitation, "stay-bonus" or similar
     arrangements or fees) to employees, stockholders or consultants (or any
     Affiliates thereof) of the Target as a result of the consummation of the
     Merger which, individually or, when taken together with related
     incurrences, commitments or obligations, exceeds $250,000; it being
     understood that if the Effective Time shall not have occurred on or prior
     to May 31, 1998, and the Agreement has not otherwise terminated in
     accordance with its terms, the Parties agree to negotiate in good faith
     with each other an appropriate extension of this covenant to relate to
     periods after May 31, 1998;".

     9.   Section 6(a)(iii) of the Amended Agreement is hereby amended and
restated in its entirety as follows:

          "(iii)  the representations and warrants set forth in (S)3 above shall
     be true and correct in all material respects at and as of the Closing Date,
     except for (A) changes contemplated by this Agreement, (B) those
     representations and warranties which address matters only as of a
     particular date (which shall have been true and correct as of such date),
     and (C) those representations and warranties set forth in
     (S)(S)3(g)(ii)(A), 3(j) and 3(l)(ii) which shall have been true and correct
     as of February 3, 1998;".

    10.   Sections 6(a)(ix) of the Amended Agreement is hereby deleted in its
entirety.

     11.  Section 6(b)(iii) of the Amended Agreement is hereby amended and
restated in its entirety as follows:

                                      -3-
<PAGE>
 
     "(iii)  the representations and warranties set forth in (S)4 above shall be
     true and correct in all material respects at and as of the Closing Date,
     except for (A) changes contemplated by this Agreement, (B) those
     representations and warranties which address matters only as of a
     particular date (which shall have been true and correct as of such date),
     and (C) those representations and warranties set forth in (S)(S)4(g), 4(i)
     and 4(j)(ii) which shall have been true and correct as of February 3,
     1998;".

     12.  The last paragraph of Section 6(a) of the Amended Agreement is hereby
amended and restated in its entirety as follows:

          "Subject to the provisions of applicable law, the Purchaser and
     Purchaser Subsidiary may waive, in whole or in part, any condition
     specified in this (S)6(a) if they execute a writing so stating at or prior
     to the Closing."

     13.  Section 7(a)(vi) of the Amended Agreement, and the definition of
"Additional Consideration" set forth in Section 1 of the Amended Agreement, are
hereby deleted in their entirety.

     14.  All capitalized terms used herein and not otherwise defined shall have
the meanings ascribed to them in the Amended Agreement.

     15.  In the case of any inconsistency or conflict between the provisions of
this Amendment No. 2 and the provisions of the Amended Agreement, the provisions
of this Amendment No. 2 shall govern.

     16.  Except as expressly provided for in this Amendment No. 2, all terms,
conditions and obligations contained in the Amended Agreement are hereby
confirmed and shall remain unchanged and in full force and effect.

     17.  Where provisions of the Amended Agreement are deleted in their
entirety, without amendment, restatement or replacement as a result of this
Amendment No. 2, the words "Intentionally Omitted" shall be inserted in their
place.

     18.  Purchaser and Purchaser Subsidiary hereby confirm to Target, and
Target hereby confirms to Purchaser and Purchaser Subsidiary, that each of them
is not aware of any conditions to Closing contained in the Amended Agreement
that it believes will not be satisfied on the Closing Date.

     19.  THIS AMENDMENT NO. 2 SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE
WITH THE LAWS OF THE STATE OF FLORIDA, WITHOUT REGARD TO SUCH STATE'S CONFLICT
OF LAWS RULES.

                                      -4-
<PAGE>
 
     IN WITNESS WHEREOF, the Parties hereto have executed this Amendment No. 2
as of the date first above written.

                              PRIMUS TELECOMMUNICATIONS
                              GROUP, INCORPORATED



                              By: /s/ K. Paul Singh
                                  -----------------------------
                              Name:   K. Paul Singh
                              Title:  Chairman, President and Chief
                                      Executive Officer



                              TAURUS ACQUISITION CORPORATION



                              By: /s/ K. Paul Singh
                                  ------------------------------
                              Name:   K. Paul Singh
                              Title:  President



                              TRESCOM INTERNATIONAL, INC.



                              By: /s/ Wesley T. O'Brien
                                  -------------------------------
                              Name:  Wesley T. O'Brien
                              Title: President and Chief Executive Officer

                                      -5-

<PAGE>
 
                                                                    EXHIBIT 99.F
                                                                    ------------

                 AMENDMENT NO. 1 TO THE STOCKHOLDER AGREEMENT
                 --------------------------------------------

          This Amendment No. 1, dated as of April 16, 1998 ("Amendment No. 1"),
                                                             ---------------   
to the Stockholder Agreement dated as of February 3, 1998 (the "Stockholder
                                                                -----------
Agreement"), is entered into by and among Warburg, Pincus Investors, L.P., a
- ---------                                                                   
Delaware limited partnership ("Stockholder"), Primus Telecommunications Group,
                               -----------                                    
Incorporated, a Delaware corporation ("Purchaser"), Taurus Acquisition
                                       ---------                      
Corporation, a Florida corporation and a wholly-owned subsidiary of Purchaser
                                                                             
("Purchaser Subsidiary"), K. Paul Singh, a resident of the Commonwealth of
- ----------------------                                                    
Virginia (the "Executive"), and, as to Section 2A.6 hereof only, TresCom
               ---------                                                
International, Inc., a Florida corporation (the "Target").  The Stockholder,
                                                 ------                     
Purchaser, Purchaser Subsidiary and Executive are referred to collectively
herein as the "Parties".  Capitalized terms not otherwise defined herein have
               -------                                                       
the meanings set forth in the Stockholder Agreement.

                                  WITNESSETH:
                                  -----------

          WHEREAS, the Parties previously entered into the Stockholder Agreement
and, together with the Target (as to Section 2A.6 hereof only) now desire to
amend the Stockholder Agreement as set forth below;

          WHEREAS, concurrently with this Amendment No. 1, and as a condition
hereto, Purchaser, Purchaser Subsidiary and Target are entering into an
amendment to the Agreement and Plan of Merger dated as of February 3, 1998 (as
so amended, as previously amended and as hereafter amended, the "Merger
                                                                 ------
Agreement");
- ---------   

          NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein, and for other good and valuable
consideration, the receipt and sufficiency of which is hereby acknowledged, the
Parties and the Target (as to Section 2A.6 hereof only) agree as follows:

     1.   Section 1.1 of the Stockholder Agreement is hereby amended by deleting
the words ", except as expressly set forth below," and the proviso appearing in
the last sentence thereof.

     2.   Section 2.1 of the Stockholder Agreement is hereby amended (i) by
deleting the words "fifty percent (50%)" and inserting in its place the words
"one hundred percent (100%)" and (ii) by deleting the words "$10 per Share" and
inserting in its place the words "$12 per Share".

     3.   A new Section 2A is hereby added to the Stockholder Agreement which
shall read in its entirety as follows:

"2A. Option
     ------

     2A.1.     Stockholder hereby grants to the Purchaser an irrevocable option,
exercisable as provided herein (the "Option"), to purchase all of the Shares
                                     ------                                 
(the "Option Shares") at an exercise price determined as set forth below.  The
      -------------                                                           
exercise price per Share shall be payable in shares of Purchaser Common Stock
(as defined 
<PAGE>

in Section 8.5 below) and shall equal the Per Share Merger Consideration (as
defined in the Merger Agreement), it being understood that for purposes of
determining the Per Share Merger Consideration in connection with this
Agreement, the Weighted Average Sales Price of a Purchaser Share shall be
determined with reference to the applicable exercise date of the Option as
opposed to the Closing Date (as defined in the Merger Agreement).

     2A.2.     The Option may be exercised by the Purchaser at any time after
the Merger Agreement is terminated under circumstances which entitle the
Purchaser to receive the amount provided for under Section 7(b)(ii) of the
Merger Agreement until the 30th day following the termination of the Merger
Agreement.  If the Purchaser wishes to exercise the Option, the Purchaser shall
give written notice to the Stockholder of its exercise of the Option, specifying
the place, time and date (not earlier than three business days and not later
than 20 days from the date such notice is given) for the closing of such
purchase (the "Closing").  If the Option is exercised, Stockholder agrees to
               -------                                                      
exercise the Warrant in full no later than immediately prior to the Closing, it
being understood that all such Shares obtained by Stockholder upon the exercise
of the Warrant shall be subject to the Option and purchased by the Purchaser at
the Closing.  The exercise of the Option shall be effective on the date such
notice of exercise is given.  The Closing shall be held on the date specified in
such notice unless, on such date, there shall be any preliminary or permanent
injunction or other order by any court of competent jurisdiction or any other
legal restraint or prohibition preventing the consummation of such purchase, in
which event the Closing shall be held as soon as practicable following the
lifting, termination or suspension of such injunction, order, restraint or
prohibition (each party agreeing to use its best efforts to have such
injunction, order, restraint or prohibition lifted, terminated or suspended),
but in any event within two days thereof.  Stockholder's obligations to sell
Option Shares upon exercise of the Option are subject to the condition that
there shall be no preliminary or permanent injunction or other order preventing
or restricting the issuance of the Option Shares to the Purchaser or the
issuance of Purchaser Common Stock to Stockholder.

     2A.3 Delivery of Exercise Price and Option Shares.  At any Closing
          --------------------------------------------                 
hereunder (a) the Purchaser shall make payment to the Stockholder of the
aggregate Exercise Price for the Option Shares so purchased by delivery of  a
certificate or certificates, duly executed by the Purchaser and registered in
the name of Stockholder, representing the number of shares of Purchaser Common
Stock as determined pursuant to this Section 2A, and (b) the Stockholder shall
deliver or cause to be delivered to the Purchaser a certificate or certificates,
duly executed by the Target and registered in the name of the Purchaser,
representing the number of Option Shares so purchased.

                                      -2-
<PAGE>

     2A.4      Offer to Other Stockholders.  Promptly after the Closing
               ---------------------------                             
hereunder, but in no event later than five (5) business days after the Closing
hereunder, Purchaser agrees to take all actions necessary or appropriate in
order to commence a tender offer (an "Offer") under the Exchange Act and the
                                      -----                                 
rules and regulations thereunder for any and all outstanding shares of Common
Stock not owned by the Purchaser, and shall use reasonable efforts to promptly
complete the Offer.  The amount and the form of the purchase price per share of
Common Stock to be paid in any such Offer shall be the same as is paid per Share
to Stockholder upon exercise of the Option.

     2A.5 Stockholder's Investment Representation.  In connection with any
          ---------------------------------------                         
exercise of the Option and the issuance of shares of Purchaser Common Stock to
Stockholder pursuant thereto, Stockholder represents and warrants to the
Purchaser  that it is an institutional "accredited investor" within the meaning
of subparagraph (a)(1), (2), (3), or (7) of Rule 501 under the Securities Act
(an "Institutional Accredited Investor") or, if the shares of Purchaser Common
Stock are to be issued to one or more accounts ("investor accounts") for which
it is acting as fiduciary or agent, each such account is an Institutional
Accredited Investor.  In the normal course of its business, it invests in or
purchases securities similar to the shares of Purchaser Common Stock and it has
such knowledge and experience in financial and business matters that it is
capable of evaluating the merits and risks of purchasing the Purchaser Common
Stock.  It is acquiring the shares of Purchaser Common Stock for its own
account, or for one or more investor accounts for which it is acting as a
fiduciary or agent, in each case for investment, and not with a view to, or for
offer or sale in connection with, any distribution thereof in violation of the
Securities Act, subject to any requirement of law that the disposition of its
property or the property of such investor account or accounts be at all times
within its or their control and subject to its or their ability to resell any
such shares of Purchaser Common Stock pursuant to any exemption from
registration available under the Securities Act or pursuant to the registration
rights granted below in this Agreement.  It understands and acknowledges that
the shares of Purchaser Common Stock will not have been registered under the
Securities Act or any other applicable securities laws and, unless so
registered, may not be offered, sold or otherwise transferred except in
compliance with the registration requirements of the Securities Act and any
other applicable securities laws, or pursuant to an exemption therefrom or in a
transaction not subject thereto. It is aware that it (or any investor account)
may be required to bear the economic risk of an investment in the shares of
Purchaser Common Stock for an indefinite period of time and it (or such account)
is able to bear that risk for an indefinite period.  It agrees that the shares
of Purchaser Common Stock will bear a legend in substantially the following
form:

     THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
     UNDER THE SECURITIES ACT OR ANY OTHER APPLICABLE
                                      -3-
<PAGE>

     SECURITIES LAWS AND, UNLESS SO REGISTERED, MAY NOT BE OFFERED, SOLD
     OR OTHERWISE TRANSFERRED EXCEPT IN COMPLIANCE WITH THE REGISTRATION
     REQUIREMENTS OF THE SECURITIES ACT AND ANY OTHER APPLICABLE
     SECURITIES LAWS, OR PURSUANT TO AN EXEMPTION THEREFROM OR IN A
     TRANSACTION NOT SUBJECT THERETO.

     2A.6 Purchaser Board Representation.  Concurrently with the Closing,
          ------------------------------                                 
Stockholder agrees to use its reasonable best efforts to cause Messrs. Douglas
Karp, Henry Kressel and Gary Nusbaum (the "Existing Stockholder Designees"), or
any person who succeeds any of the Existing Stockholder Designees as a member of
the Target's board of directors and who is designated by Stockholder, other than
those persons designated by the Purchaser as provided below (the "Stockholder
Designees"), to resign immediately from the Target's board of directors.
Subject to applicable law and the charter and by-laws of the Target, immediately
after such resignation of the Stockholder Designees, the Target agrees to use
its reasonable best efforts (a) to take such actions as are necessary or
appropriate to increase the number of persons to serve as directors of the
Target and (b) to cause to be appointed to its board of directors such number of
designees of the Purchaser (all of whom are reasonably acceptable to the Target
board of directors) so that, after giving effect to such increase and
appointment, the designees of Purchaser so appointed shall constitute a majority
of the members of the Target's board of directors.  The Target hereby agrees
that if any of the Existing Stockholder Designees resigns, is removed or is
otherwise no longer serving as a member of the Target's board of directors, in
each case prior to the Closing, it will use its reasonable best efforts to cause
any such vacancy in the Target's board of directors to be filled by an
individual who is an employee or affiliate of the Stockholder."

      4.       Section 5 of the Stockholder Agreement is hereby amended and
restated to read in its entirety as follows:

     "5.  Termination.  This Agreement shall terminate on the earliest of (a)
          -----------                                                        
the Effective Time (as defined in the Merger Agreement), (b) the date
immediately following the termination of the Merger Agreement in accordance with
its terms, and (c) October 31, 1998; provided, however, (i) the provisions of
Section 1.1 shall survive any termination of this Agreement for so long as the
Option remains exercisable, (ii) the provisions of Sections 2, 2A, 5 and 6 shall
survive any termination of this Agreement, and (iii) the provisions of Sections
8.3, 8.4, 8.5, 8.7 and 9 shall survive (x) the Effective Time if this Agreement
otherwise terminates at the Effective Time or (y) if the Option is exercisable
or exercised under Section 2A and this Agreement otherwise terminates."

     5.   The definition of "Registrable Securities" set forth in Section 9.1 of
the Stockholder Agreement is amended and restated to read in its entirety as
follows:

                                      -4-
<PAGE>

          "'Registrable Securities' means all the Purchaser Shares received by
            ----------------------                                            
the Stockholder at the Effective Time or pursuant to any exercise of the Option,
together with any additional Purchaser Shares received by the Stockholder as a
result of any stock dividend, extraordinary dividend or distribution, split-up,
recapitalization, combination, exchange of shares or the like and involving the
Purchaser Shares received by the Stockholder at the Effective Time or pursuant
to any exercise of the Option; provided, however, such securities shall cease to
be Registrable Securities when they become freely saleable to the public under
Rule 145(d) and Rule 144, without volume limitation, as the case may be."

       6.   Clause (iii) of Section 9.3(d) of the Stockholder Agreement is
amended and restated to read in its entirety as follows:

"third, to the extent additional Purchaser Shares may be included, the
Registrable Securities sought to be sold by Stockholder and any Purchaser Shares
sought to be sold by Messrs. Wesley O'Brien or Rudolph McGlashan pursuant to the
voting agreements, each dated as of February 3, 1998, as amended on April 16,
1998, pro rata among Stockholder and Messrs. O'Brien and McGlashan based upon
the number  of Purchaser Shares so sought to be sold by each of them"

      7.    The Purchaser's address for notices and other communications under
Section 11 of the Stockholder Agreement is hereby amended as follows:

                    "If to Purchaser:

                    Primus Telecommunications Group, Incorporated
                    1700 Old Meadow Road
                    McLean, VA 22102
                    Attention: K. Paul Singh, Chairman, President and CEO
                    Facsimile:  (703) 902-2814"

      8.    In the case of any inconsistency or conflict between the provisions
of this Amendment No. 1 and the provisions of the Stockholder Agreement, the
provisions of this Amendment No. 1 shall govern.

      9.    Except as expressly provided for in this Amendment No. 1, all terms,
conditions and obligations contained in the Stockholder Agreement are hereby
confirmed and shall remain unchanged and in full force and effect.

     10.    This Amendment No. 1 may be executed by facsimile signature which
shall be deemed to be an original for all purposes and may be executed in any
number of counterparts, 

                                      -5-
<PAGE>

each of which shall be deemed to be an original and all of which, when taken
together, shall constitute but one and the same instrument.
 
     11.   THIS AMENDMENT NO. 1 SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE
WITH THE LAWS OF THE STATE OF FLORIDA, WITHOUT REGARD TO SUCH STATE'S CONFLICTS
OF LAWS RULES.

                                      -6-
<PAGE>

     IN WITNESS WHEREOF, the Parties have executed this Amendment No. 1 as of
the date first above written.


                              Primus Telecommunications Group, Incorporated


                              By:   /s/ K. Paul Singh
                                    ----------------------------
                              Name:     K. Paul Singh
                              Title:    President, Chairman and Chief Executive
                                        Officer


                              Taurus Acquisition Corporation


                              By:   /s/ K. Paul Singh
                                    ----------------------------
                              Name:     K. Paul Singh
                              Title:    President


                              Warburg, Pincus, Investors, L.P.

                              By:   Warburg, Pincus & Co., general partner


                                    By:  /s/ Douglas Karp
                                         ------------------------------
                                    Name:    Douglas Karp
                                    Title:



                                    /s/ K. Paul Singh
                                    -----------------------------
                                        K. Paul Singh

                              AS TO SECTION 2A.6 ONLY:

                              TresCom International, Inc.


                              By:   /s/ Wesley T. O'Brien
                                    -----------------------------
                              Name:     Wesley T. O'Brien
                              Title:    President and Chief Executive Officer

                                      -7-

<PAGE>
 
                                                                    EXHIBIT 99.G
                                                                    ------------
 
                    AMENDMENT NO. 1 TO THE VOTING AGREEMENT
                    ---------------------------------------

          This Amendment No. 1, dated as of April 16, 1998 ("Amendment No. 1"),
                                                             ---------------   
to the Voting Agreement dated as of February 3, 1998 (the "Voting Agreement"),
                                                           ----------------   
is entered into by and between the person identified as a Shareholder of TRESCOM
INTERNATIONAL, INC., a Florida corporation (the "Company"), on the signature
                                                 -------                    
page below (the "Shareholder") and PRIMUS TELECOMMUNICATIONS GROUP,
                 -----------                                       
INCORPORATED, a Delaware corporation (the "Purchaser").  The Shareholder and the
                                           ---------                            
Purchaser are referred to collectively herein as the "Parties".  Capitalized
                                                      -------               
terms not otherwise defined herein have the meanings set forth in the Voting
Agreement.

                                  WITNESSETH:
                                  -----------

          WHEREAS, the Parties previously entered into a Voting Agreement and
now desire to amend the Voting Agreement as set forth below;

          WHEREAS, concurrently with this Amendment No. 1, and as a condition
hereto, Purchaser, the Company and Taurus Acquisition Corporation, a Florida
corporation and wholly-owned subsidiary of the Purchaser ("Purchaser
                                                           ---------
Subsidiary"), are entering into an amendment to the Agreement and Plan of Merger
dated as of February 3, 1998 (as so amended, as previously amended and as
hereafter amended, the "Merger Agreement");
                        ----------------   

          NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein, and for other good and valuable
consideration, the receipt and sufficiency of which is hereby acknowledged, the
Parties agree as follows:

          1. Section 1 of the Voting Agreement is hereby amended to delete the
last sentence thereof.

          2. The Voting Agreement is hereby amended to create a new Section 20
which shall read in its entirety:

"20. Purchaser Option
     ----------------

     20.1.     Shareholder hereby grants to the Purchaser an irrevocable option,
exercisable as provided herein (the "Purchaser Option"), to purchase all of the
                                     ----------------                          
Shares (the "Purchaser Option Shares") at an exercise price determined as set
             -----------------------                                         
forth below.  The exercise price per Share shall be payable in shares of common
stock, par value $.01 per share, of the Purchaser ("Purchaser Common Stock",
                                                    ----------------------  
each a "Purchaser Share") and shall equal the Per Share Merger Consideration (as
        ---------------                                                         
defined in the Merger Agreement), it being understood that for purposes of
determining the Per Share Merger Consideration in connection with this
Agreement, the Weighted Average Sales Price (as defined in the Merger Agreement)
of a Purchaser Share shall be determined with reference to the applicable
exercise date of the Purchaser Option as opposed to the Closing Date (as defined
in the Merger Agreement).
<PAGE>
 
     20.2. The Purchaser Option may be exercised by the Purchaser at any
time after the Merger Agreement is terminated under circumstances which entitle
the Purchaser to receive the amount provided for under Section 7(b)(ii) of the
Merger Agreement until the 30th day following the termination of the Merger
Agreement.  If the Purchaser wishes to exercise the Purchaser Option, the
Purchaser shall give written notice to the Shareholder of its exercise of the
Purchaser Option, specifying the place, time and date, not earlier than three
business days and not later than 20 days from the date such notice is given, for
the closing of such purchase (the "Closing").  The exercise of the Purchaser
                                   -------                                  
Option shall be effective on the date such notice of exercise is given.  The
Closing shall be held on the date specified in such notice unless, on such date,
there shall be any preliminary or permanent injunction or other order by any
court of competent jurisdiction or any other legal restraint or prohibition
preventing the consummation of such purchase, in which event the Closing shall
be held as soon as practicable following the lifting, termination or suspension
of such injunction, order, restraint or prohibition (each party agreeing to use
its best efforts to have such injunction, order, restraint or prohibition
lifted, terminated or suspended), but in any event within two days thereof.
Shareholder's obligations to sell Purchaser Option Shares upon exercise of the
Purchaser Option are subject to the condition that there shall be no preliminary
or permanent injunction or other order preventing or restricting the issuance of
the Purchaser Option Shares to the Purchaser or the issuance of Purchaser Common
Stock to Shareholder.

     20.3 Delivery of Exercise Price and Purchaser Option Shares.  At any
          ------------------------------------------------------         
Closing hereunder (a) the Purchaser shall make payment to the Shareholder of the
aggregate Exercise Price for the Purchaser Option Shares so purchased by
delivery of a certificate or certificates duly executed by the Purchaser and
registered in the name of Shareholder, representing the number of shares of
Purchaser Common Stock as determined pursuant to this Section 20, and (b) the
Shareholder shall deliver or cause to be delivered to the Purchaser a
certificate or certificates, duly executed by the Company and registered in the
name of the Purchaser, representing the number of Purchaser Option Shares so
purchased."

     20.4 Shareholder's Investment Representation.  In connection with any
          ---------------------------------------                         
exercise of the Purchaser Option and the issuance of shares of Purchaser Common
Stock to Shareholder pursuant thereto, Shareholder represents and warrants to
the Purchaser that he is an "accredited investor" within the meaning of Rule 501
under the Securities Act (an "Accredited Investor").  Shareholder has such
knowledge and experience in financial and business matters that he is capable of
evaluating the merits and risks of the transactions contemplated hereby.  He is
acquiring the shares of Purchaser Common Stock for his own account, and not with
a view to, or for offer or sale in connection with, any distribution thereof in
violation of the Securities Act of 1933, as amended (the "Securities Act"),
                                                          --------------   
subject to any requirement of law that the disposition of his property be at all
times within his control and subject to his ability to resell any such shares of
Purchaser Common Stock pursuant to any exemption from registration available
under the Securities Act or pursuant to the registration

                                       2
<PAGE>
 
rights granted below in this Agreement.  He understands and acknowledges that
the shares of Purchaser Common Stock will not have been registered under the
Securities Act or any other applicable securities laws and, unless so
registered, may not be offered, sold or otherwise transferred except in
compliance with the registration requirements of the Securities Act and any
other applicable securities laws, or pursuant to an exemption therefrom or in a
transaction not subject thereto. He is aware that he may be required to bear the
economic risk of an investment in the shares of Purchaser Common Stock for an
indefinite period of time and he is able to bear that risk for an indefinite
period.  He agrees that the shares of Purchaser Common Stock will bear a legend
in substantially the following form:

     THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER
     THE SECURITIES ACT OR ANY OTHER APPLICABLE SECURITIES LAWS AND, UNLESS SO
     REGISTERED, MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED EXCEPT IN
     COMPLIANCE WITH THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND ANY
     OTHER APPLICABLE SECURITIES LAWS, OR PURSUANT TO AN EXEMPTION THEREFROM OR
     IN A TRANSACTION NOT SUBJECT THERETO."

      3.       Section 4 of the Voting Agreement is hereby amended and restated
to read in its entirety, as follows:

     "4.  Termination.  This Agreement shall terminate on the earliest of (a)
          -----------                                                        
the Effective Time (as defined in the Merger Agreement), (b) the date
immediately following the termination of the Merger Agreement in accordance with
its terms, and (c) October 31, 1998; provided, however, (i) the provisions of
Section 1 shall survive any termination of this Agreement for so long as the
Purchaser Option remains exercisable pursuant to Section 20, (ii) the provisions
of Sections 5, 6 and 20 shall survive any termination of this Agreement, (iii)
the provisions of Section 21 shall survive (x) the Effective Time if this
Agreement otherwise terminates at the Effective Time or (y) if the Purchaser
Option is exercisable or exercised pursuant to Section 20 and this Agreement
otherwise terminates and (iv) the provisions of Section 22 shall survive if the
Purchaser Option is exercisable or exercised pursuant to Section 20 and this
Agreement otherwise terminates."

      4.       The Voting Agreement is hereby amended to create a new Section 21
which shall read in its entirety:

"21. Piggyback Registration.
     ---------------------- 

     21.1 Definitions.  As used herein, unless the context otherwise requires,
          -----------                                                         
the following terms have the following respective meanings:

          "Commission"  means the United States Securities and Exchange
           ----------                                                  
Commission.

                                       3
<PAGE>
 
          "Registrable Securities" means all the Purchaser Shares received by
           ----------------------                                            
the Shareholder at the Effective Time or pursuant to any exercise of the
Purchaser Option, together with any additional Purchaser Shares received by the
Shareholder as a result of any stock dividend, extraordinary dividend or
distribution, split-up, recapitalization, combination, exchange of shares or the
like and involving the Purchaser Shares received by the Shareholder at the
Effective Time or pursuant to any exercise of the Purchaser Option; provided,
however, such securities shall cease to be Registrable Securities when they
become freely saleable to the public under Rule 145(d) and Rule 144, without
volume limitation, as the case may be.

          "Registration Expenses" means all expenses incurred by the Purchaser
           ---------------------                                              
incident to the Purchaser's performance of this Section 21, including, without
limitation, all registration, filing and National Association of Securities
Dealers, Inc. fees, all listing fees, all fees and expenses of complying with
securities or blue sky laws (including, without limitation, reasonable fees and
disbursements of counsel for the underwriters in connection with blue sky
qualifications of the Registrable Securities), all printing expenses, the fees
and disbursements of counsel for the Purchaser and of the Purchaser's
independent public accountants, including the expenses of "comfort" letters, its
expenses incurred in connection with any "road show" presentations in which it
may participate and any fees and disbursements of underwriters customarily paid
by issuers or sellers of securities.

          "Selling Expenses" means all expenses incurred by the Shareholder
           ----------------                                                
incident to the Shareholder's performance of this Section 21, including, without
limitation, all underwriting discounts and commissions, the fees and
disbursements of its advisors, including its counsel and its accountants, and
its expenses incurred in connection with any "road show" presentations in which
it may participate.

     21.2 Right to Include Registrable Securities.  If the Purchaser at any time
          ---------------------------------------                               
proposes to register any of its securities under the Securities Act by
registration on Forms S-1, S-2, S-3 or any successor or similar form(s) (except
registrations on such forms or similar forms solely for registration of
securities in connection with (i) an employee benefit plan or dividend
reinvestment plan or a merger or consolidation or (ii) debt securities which are
not convertible into Purchaser Common Stock), whether or not for sale for its
own account, it shall each such time give written notice to the Shareholder of
its intention to do so at least 30 days prior to the anticipated filing date of
a registration statement with respect to such registration with the Commission.
Upon the written request of the Shareholder made as promptly as practicable and
in any event within 10 business days after the receipt of any such notice, which
request shall specify the Registrable Securities intended to be disposed of by
the Shareholder, the Purchaser shall use reasonable efforts to effect the
registration under the Securities Act of all Registrable Securities which the
Purchaser has been so requested to register by the Shareholder; provided,
however, that if, at any time after giving written notice of its intention to
register any securities and prior to the effective date of the registration
statement filed in

                                       4
<PAGE>
 
connection with such registration, the Purchaser shall determine for any reason
not to register or to delay registration of such securities, the Purchaser may,
at its election, give written notice of such determination to the Shareholder
and (i) in the case of a determination not to register, shall be relieved of its
obligation to register any Registrable Securities in connection with such
registration, without prejudice, and (ii) in the case of a determination to
delay registering, shall be permitted to delay registering any Registrable
Securities for the same period as the delay in registering such other
securities. If an underwritten offering, any right of the Shareholder to
participate in a registration pursuant to this Section 21.2 shall be conditioned
upon it agreeing to offer and sell Registrable Securities in accordance with the
plan of distribution applicable to the other Purchaser Shares sought to be
offered and sold in such registration.

          (b) Expenses.  The Purchaser shall pay the Registration Expenses in
              --------                                                       
connection with any registration effected pursuant to this Section 21.2 and the
Shareholder shall pay the Selling Expenses in connection with any registration
effected pursuant to this Section 21.2.

          (c) Selection of Underwriters and Form of Registration Statement.  In
              ------------------------------------------------------------     
connection with each public offering effected pursuant to this Section 21.2, the
Purchaser shall promptly select the managing underwriters, if any, and the form
of registration statement to be used in connection with any such offering.

          (d) Priority in Piggyback Registrations.  Notwithstanding anything in
              -----------------------------------                              
Section 21.2 above to the contrary, if the managing underwriter of any
underwritten public offering shall inform the Purchaser by letter of its belief
that the number or type of Registrable Securities requested to be included in
such registration would materially and adversely affect such public offering,
then the Purchaser shall promptly notify the Shareholder of such fact.  If the
managing underwriter does not agree to include all (or such lesser amount as the
Shareholder shall, in its discretion, agree to) of the number of the Registrable
Securities initially requested by the Shareholder to be included in such
registration, then the Purchaser shall include in such registration, to the
extent of the number and type which the Purchaser is so advised can be sold in
such Public Offering, (i) first, the Purchaser Shares proposed to be sold by
Purchaser; (ii) second, to the extent additional Purchaser Shares may be
included, the Purchaser Shares proposed to be sold by any members of Quantum
Industrial Partners LDC, S-C Phoenix Holdings, L.L.C., Winston Partners II LDC
and Winston Partners II LLC (collectively, the "Chaterjee Group"), or any of
                                                ---------------             
their respective affiliates or transferees, and (iii) third, to the extent
additional Purchaser Shares may be included, the Registrable Securities sought
to be sold by the Shareholder, Purchaser Shares sought to be sold by Warburg,
Pincus Investors, LP ("Warburg, Pincus"), and Ruddy McGlashan, pro rata among
the Shareholder, Warburg, Pincus and Mr. McGlashan based on the number of
Purchaser Shares so sought to be sold by each of them.  In the event that the
proposed registration by Purchaser is pursuant to a contractual demand

                                       5
<PAGE>
 
registration right, the sale of Purchaser Shares by such party making the demand
or by any member of the Chaterjee Group shall have priority over the sale of the
Registrable Securities."

      5.       The Voting Agreement is hereby amended to create a new Section 22
which shall read in its entirety:

"22. Put Option.
     ---------- 

     22.1 If, upon exercise of the Purchaser Option, Shareholder receives
"restricted securities" within the meaning of Rule 144 under the Securities Act,
Purchaser hereby grants to Shareholder an irrevocable option, exercisable as
provided herein (the "Put Option"), to sell all of the Purchaser Shares acquired
                      ----------                                                
by the Shareholder in conjunction with the exercise of the Purchaser Option, at
an exercise price determined as set forth below.  The exercise price per
Purchaser Share shall be payable in cash and shall equal the Weighted Average
Sales Price of the Purchaser Shares as determined with reference to the
applicable exercise date of the Purchaser Option (the "Put Option
                                                       ----------
Consideration").  The Put Option Consideration shall be subject to proportionate
adjustment in the event of any stock split, stock dividend or reverse stock
split.

     22.2 The Put Option may be exercised by the Shareholder, in whole or in
part, from time to time by providing notice to the Purchaser.  Notice of the
Shareholder's intent to exercise the Put Option must be received by the
Purchaser within thirty (30) calendar days from the date on which the Purchaser
Option is exercised and must include the number of Purchaser Shares to be
subject to the Put Option.  Failure to notify the Purchaser within such 30-day
period shall terminate any rights and duties under this provision.  The closing
under any such exercise shall take place at the Purchaser's executive offices
twenty (20) days after the date on which the Purchaser first receives notice
from the Shareholder."

      6.    The Purchaser's address for notices and other communications under
Section 11 of the Voting Agreement is hereby amended as follows:

                    "If to Purchaser:

                    Primus Telecommunications Group, Incorporated
                    1700 Old Meadow Road
                    McLean, VA 22102
                    Attention: K. Paul Singh, Chairman, President and CEO
                    Facsimile:  (703) 902-2814"

     7.   In the case of any inconsistency or conflict between the provisions of
this Amendment No. 1 and the provisions of the Voting Agreement, the provisions
of this Amendment No. 1 shall govern.

                                       6
<PAGE>
 
          Except as expressly provided for in this Amendment No. 1, all terms,
conditions and obligations contained in the Voting Agreement are hereby
confirmed and shall remain unchanged and in full force and effect.

          This Amendment No. 1 may be executed by facsimile signature which
shall be deemed to be an original for all purposes and may be executed in any
number of counterparts, each of which shall be deemed to be an original and all
of which, when taken together, shall constitute but one and the same instrument.

          THIS AMENDMENT NO. 1 SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE
WITH THE LAWS OF THE STATE OF FLORIDA, WITHOUT REGARD TO SUCH STATE'S CONFLICTS
OF LAWS RULES.

                                       7
<PAGE>
 
          IN WITNESS WHEREOF, the Purchaser has caused this Amendment No. 1 to
be executed by its duly authorized officers, and the Shareholder has duly
executed this Amendment No. 1, each as of the date and year first above written.


                    PURCHASER:

                    PRIMUS TELECOMMUNICATIONS GROUP, INCORPORATED
 

                    By:  /s/ K. Paul Singh
                         -------------------------------------
                         K. Paul Singh, Chief Executive Officer
 

                    SHAREHOLDER:


                         /s/ Wesley T. O'Brien
                    ______________________________________
                         Wesley T. O'Brien

                                       8

<PAGE>
 
                                                                    EXHIBIT 99.H
                                                                    ------------

                    AMENDMENT NO. 1 TO THE VOTING AGREEMENT
                    ---------------------------------------

          This Amendment No. 1, dated as of April 16, 1998 ("Amendment No. 1"),
                                                             ---------------   
to the Voting Agreement dated as of February 3, 1998 (the "Voting Agreement"),
                                                           ----------------   
is entered into by and between the person identified as a Shareholder of TRESCOM
INTERNATIONAL, INC., a Florida corporation (the "Company"), on the signature
                                                 -------                    
page below (the "Shareholder") and PRIMUS TELECOMMUNICATIONS GROUP,
                 -----------                                       
INCORPORATED, a Delaware corporation (the "Purchaser").  The Shareholder and the
                                           ---------                            
Purchaser are referred to collectively herein as the "Parties".  Capitalized
                                                      -------               
terms not otherwise defined herein have the meanings set forth in the Voting
Agreement.

                                  WITNESSETH:
                                  -----------

          WHEREAS, the Parties previously entered into a Voting Agreement and
now desire to amend the Voting Agreement as set forth below;

          WHEREAS, concurrently with this Amendment No. 1, and as a condition
hereto, Purchaser, the Company and Taurus Acquisition Corporation, a Florida
corporation and wholly-owned subsidiary of the Purchaser ("Purchaser
                                                           ---------
Subsidiary"), are entering into an amendment to the Agreement and Plan of Merger
dated as of February 3, 1998 (as so amended, as previously amended and as
hereafter amended, the "Merger Agreement");
                        ----------------   

          NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein, and for other good and valuable
consideration, the receipt and sufficiency of which is hereby acknowledged, the
Parties agree as follows:

          1.   Section 1 of the Voting Agreement is hereby amended to delete the
last sentence thereof.

          2.   The Voting Agreement is hereby amended to create a new Section 20
which shall read in its entirety:

"20. Purchaser Option
     ----------------

      20.1.   Shareholder hereby grants to the Purchaser an irrevocable option,
exercisable as provided herein (the "Purchaser Option"), to purchase all of the
                                     ----------------                          
Shares (the "Purchaser Option Shares") at an exercise price determined as set
             -----------------------                                         
forth below.  The exercise price per Share shall be payable in shares of common
stock, par value $.01 per share, of the Purchaser ("Purchaser Common Stock",
                                                    ----------------------  
each a "Purchaser Share") and shall equal the Per Share Merger Consideration (as
        ---------------                                                         
defined in the Merger Agreement), it being understood that for purposes of
determining the Per Share Merger Consideration in connection with this
Agreement, the Weighted Average Sales Price (as defined in the Merger Agreement)
of a Purchaser Share shall be determined with reference to the applicable
exercise date of the Purchaser Option as opposed to the Closing Date (as defined
in the Merger Agreement).
<PAGE>
 
     20.2.     The Purchaser Option may be exercised by the Purchaser at any
time after the Merger Agreement is terminated under circumstances which entitle
the Purchaser to receive the amount provided for under Section 7(b)(ii) of the
Merger Agreement until the 30th day following the termination of the Merger
Agreement.  If the Purchaser wishes to exercise the Purchaser Option, the
Purchaser shall give written notice to the Shareholder of its exercise of the
Purchaser Option, specifying the place, time and date, not earlier than three
business days and not later than 20 days from the date such notice is given, for
the closing of such purchase (the "Closing").  The exercise of the Purchaser
                                   -------                                  
Option shall be effective on the date such notice of exercise is given.  The
Closing shall be held on the date specified in such notice unless, on such date,
there shall be any preliminary or permanent injunction or other order by any
court of competent jurisdiction or any other legal restraint or prohibition
preventing the consummation of such purchase, in which event the Closing shall
be held as soon as practicable following the lifting, termination or suspension
of such injunction, order, restraint or prohibition (each party agreeing to use
its best efforts to have such injunction, order, restraint or prohibition
lifted, terminated or suspended), but in any event within two days thereof.
Shareholder's obligations to sell Purchaser Option Shares upon exercise of the
Purchaser Option are subject to the condition that there shall be no preliminary
or permanent injunction or other order preventing or restricting the issuance of
the Purchaser Option Shares to the Purchaser or the issuance of Purchaser Common
Stock to Shareholder.

     20.3 Delivery of Exercise Price and Purchaser Option Shares.  At any
          ------------------------------------------------------         
Closing hereunder (a) the Purchaser shall make payment to the Shareholder of the
aggregate Exercise Price for the Purchaser Option Shares so purchased by
delivery of a certificate or certificates duly executed by the Purchaser and
registered in the name of Shareholder, representing the number of shares of
Purchaser Common Stock as determined pursuant to this Section 20, and (b) the
Shareholder shall deliver or cause to be delivered to the Purchaser a
certificate or certificates, duly executed by the Company and registered in the
name of the Purchaser, representing the number of Purchaser Option Shares so
purchased."

     20.4 Shareholder's Investment Representation.  In connection with any
          ---------------------------------------                         
exercise of the Purchaser Option and the issuance of shares of Purchaser Common
Stock to Shareholder pursuant thereto, Shareholder represents and warrants to
the Purchaser that he is an "accredited investor" within the meaning of Rule 501
under the Securities Act (an "Accredited Investor").  Shareholder has such
knowledge and experience in financial and business matters that he is capable of
evaluating the merits and risks of the transactions contemplated hereby.  He is
acquiring the shares of Purchaser Common Stock for his own account, and not with
a view to, or for offer or sale in connection with, any distribution thereof in
violation of the Securities Act of 1933, as amended (the "Securities Act"),
                                                          --------------   
subject to any requirement of law that the disposition of his property be at all
times within his control and subject to his ability to resell any such shares of
Purchaser Common Stock pursuant to any exemption from registration available
under the Securities Act or pursuant to the registration

                                       2
<PAGE>
 
rights granted below in this Agreement.  He understands and acknowledges that
the shares of Purchaser Common Stock will not have been registered under the
Securities Act or any other applicable securities laws and, unless so
registered, may not be offered, sold or otherwise transferred except in
compliance with the registration requirements of the Securities Act and any
other applicable securities laws, or pursuant to an exemption therefrom or in a
transaction not subject thereto. He is aware that he may be required to bear the
economic risk of an investment in the shares of Purchaser Common Stock for an
indefinite period of time and he is able to bear that risk for an indefinite
period.  He agrees that the shares of Purchaser Common Stock will bear a legend
in substantially the following form:

     THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER
     THE SECURITIES ACT OR ANY OTHER APPLICABLE SECURITIES LAWS AND, UNLESS SO
     REGISTERED, MAY NOT BE OFFERED, SOLD OR OTHERWISE TRANSFERRED EXCEPT IN
     COMPLIANCE WITH THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND ANY
     OTHER APPLICABLE SECURITIES LAWS, OR PURSUANT TO AN EXEMPTION THEREFROM OR
     IN A TRANSACTION NOT SUBJECT THERETO."

     3.   Section 4 of the Voting Agreement is hereby amended and restated
to read in its entirety, as follows:

     "4.  Termination.  This Agreement shall terminate on the earliest of (a)
          -----------                                                        
the Effective Time (as defined in the Merger Agreement), (b) the date
immediately following the termination of the Merger Agreement in accordance with
its terms, and (c) October 31, 1998; provided, however, (i) the provisions of
Section 1 shall survive any termination of this Agreement for so long as the
Purchaser Option remains exercisable pursuant to Section 20, (ii) the provisions
of Sections 5, 6 and 20 shall survive any termination of this Agreement, (iii)
the provisions of Section 21 shall survive (x) the Effective Time if this
Agreement otherwise terminates at the Effective Time or (y) if the Purchaser
Option is exercisable or exercised pursuant to Section 20 and this Agreement
otherwise terminates and (iv) the provisions of Section 22 shall survive if the
Purchaser Option is exercisable or exercised pursuant to Section 20 and this
Agreement otherwise terminates."

      4.   The Voting Agreement is hereby amended to create a new Section 21
which shall read in its entirety:

"21. Piggyback Registration.
     ---------------------- 

     21.1 Definitions.  As used herein, unless the context otherwise requires,
          -----------                                                         
the following terms have the following respective meanings:

          "Commission"  means the United States Securities and Exchange
           ----------                                                  
Commission.

                                       3
<PAGE>
 
          "Registrable Securities" means all the Purchaser Shares received by
           ----------------------                                            
the Shareholder at the Effective Time or pursuant to any exercise of the
Purchaser Option, together with any additional Purchaser Shares received by the
Shareholder as a result of any stock dividend, extraordinary dividend or
distribution, split-up, recapitalization, combination, exchange of shares or the
like and involving the Purchaser Shares received by the Shareholder at the
Effective Time or pursuant to any exercise of the Purchaser Option; provided,
however, such securities shall cease to be Registrable Securities when they
become freely saleable to the public under Rule 145(d) and Rule 144, without
volume limitation, as the case may be.

          "Registration Expenses" means all expenses incurred by the Purchaser
           ---------------------                                              
incident to the Purchaser's performance of this Section 21, including, without
limitation, all registration, filing and National Association of Securities
Dealers, Inc. fees, all listing fees, all fees and expenses of complying with
securities or blue sky laws (including, without limitation, reasonable fees and
disbursements of counsel for the underwriters in connection with blue sky
qualifications of the Registrable Securities), all printing expenses, the fees
and disbursements of counsel for the Purchaser and of the Purchaser's
independent public accountants, including the expenses of "comfort" letters, its
expenses incurred in connection with any "road show" presentations in which it
may participate and any fees and disbursements of underwriters customarily paid
by issuers or sellers of securities.

          "Selling Expenses" means all expenses incurred by the Shareholder
           ----------------                                                
incident to the Shareholder's performance of this Section 21, including, without
limitation, all underwriting discounts and commissions, the fees and
disbursements of its advisors, including its counsel and its accountants, and
its expenses incurred in connection with any "road show" presentations in which
it may participate.

     21.2 Right to Include Registrable Securities.  If the Purchaser at any time
          ---------------------------------------                               
proposes to register any of its securities under the Securities Act by
registration on Forms S-1, S-2, S-3 or any successor or similar form(s) (except
registrations on such forms or similar forms solely for registration of
securities in connection with (i) an employee benefit plan or dividend
reinvestment plan or a merger or consolidation or (ii) debt securities which are
not convertible into Purchaser Common Stock), whether or not for sale for its
own account, it shall each such time give written notice to the Shareholder of
its intention to do so at least 30 days prior to the anticipated filing date of
a registration statement with respect to such registration with the Commission.
Upon the written request of the Shareholder made as promptly as practicable and
in any event within 10 business days after the receipt of any such notice, which
request shall specify the Registrable Securities intended to be disposed of by
the Shareholder, the Purchaser shall use reasonable efforts to effect the
registration under the Securities Act of all Registrable Securities which the
Purchaser has been so requested to register by the Shareholder; provided,
however, that if, at any time after giving written notice of its intention to
register any securities and prior to the effective date of the registration
statement filed in 

                                       4
<PAGE>
 
connection with such registration, the Purchaser shall determine for any reason
not to register or to delay registration of such securities, the Purchaser may,
at its election, give written notice of such determination to the Shareholder
and (i) in the case of a determination not to register, shall be relieved of its
obligation to register any Registrable Securities in connection with such
registration, without prejudice, and (ii) in the case of a determination to
delay registering, shall be permitted to delay registering any Registrable
Securities for the same period as the delay in registering such other
securities. If an underwritten offering, any right of the Shareholder to
participate in a registration pursuant to this Section 21.2 shall be conditioned
upon it agreeing to offer and sell Registrable Securities in accordance with the
plan of distribution applicable to the other Purchaser Shares sought to be
offered and sold in such registration.

          (b) Expenses.  The Purchaser shall pay the Registration Expenses in
              --------                                                       
connection with any registration effected pursuant to this Section 21.2 and the
Shareholder shall pay the Selling Expenses in connection with any registration
effected pursuant to this Section 21.2.

          (c) Selection of Underwriters and Form of Registration Statement.  In
              ------------------------------------------------------------     
connection with each public offering effected pursuant to this Section 21.2, the
Purchaser shall promptly select the managing underwriters, if any, and the form
of registration statement to be used in connection with any such offering.

          (d) Priority in Piggyback Registrations.  Notwithstanding anything in
              -----------------------------------                              
Section 21.2 above to the contrary, if the managing underwriter of any
underwritten public offering shall inform the Purchaser by letter of its belief
that the number or type of Registrable Securities requested to be included in
such registration would materially and adversely affect such public offering,
then the Purchaser shall promptly notify the Shareholder of such fact.  If the
managing underwriter does not agree to include all (or such lesser amount as the
Shareholder shall, in its discretion, agree to) of the number of the Registrable
Securities initially requested by the Shareholder to be included in such
registration, then the Purchaser shall include in such registration, to the
extent of the number and type which the Purchaser is so advised can be sold in
such Public Offering, (i) first, the Purchaser Shares proposed to be sold by
Purchaser; (ii) second, to the extent additional Purchaser Shares may be
included, the Purchaser Shares proposed to be sold by any members of Quantum
Industrial Partners LDC, S-C Phoenix Holdings, L.L.C., Winston Partners II LDC
and Winston Partners II LLC (collectively, the "Chaterjee Group"), or any of
                                                ---------------             
their respective affiliates or transferees, and (iii) third, to the extent
additional Purchaser Shares may be included, the Registrable Securities sought
to be sold by the Shareholder, Purchaser Shares sought to be sold by Warburg,
Pincus Investors, LP ("Warburg, Pincus"), and Wesley T. O'Brien, pro rata among
the Shareholder, Warburg, Pincus and Mr. O'Brien based on the number of
Purchaser Shares so sought to be sold by each of them.  In the event that the
proposed registration by Purchaser is pursuant to a contractual demand
registration 

                                       5
<PAGE>
 
right, the sale of Purchaser Shares by such party making the demand or by any
member of the Chaterjee Group shall have priority over the sale of the
Registrable Securities."

     5.    The Voting Agreement is hereby amended to create a new Section 22
which shall read in its entirety:

"22. Put Option.
     ---------- 

     22.1 If, upon exercise of the Purchaser Option, Shareholder receives
"restricted securities" within the meaning of Rule 144 under the Securities Act,
Purchaser hereby grants to Shareholder an irrevocable option, exercisable as
provided herein (the "Put Option"), to sell all of the Purchaser Shares acquired
                      ----------                                                
by the Shareholder in conjunction with the exercise of the Purchaser Option, at
an exercise price determined as set forth below.  The exercise price per
Purchaser Share shall be payable in cash and shall equal the Weighted Average
Sales Price of the Purchaser Shares as determined with reference to the
applicable exercise date of the Purchaser Option (the "Put Option
                                                       ----------
Consideration").  The Put Option Consideration shall be subject to proportionate
adjustment in the event of any stock split, stock dividend or reverse stock
split.

     22.2 The Put Option may be exercised by the Shareholder, in whole or in
part, from time to time by providing notice to the Purchaser.  Notice of the
Shareholder's intent to exercise the Put Option must be received by the
Purchaser within thirty (30) calendar days from the date on which the Purchaser
Option is exercised and must include the number of Purchaser Shares to be
subject to the Put Option.  Failure to notify the Purchaser within such 30-day
period shall terminate any rights and duties under this provision.  The closing
under any such exercise shall take place at the Purchaser's executive offices
twenty (20) days after the date on which the Purchaser first receives notice
from the Shareholder."

      6.   The Purchaser's address for notices and other communications under
Section 11 of the Voting Agreement is hereby amended as follows:

                    "If to Purchaser:

                    Primus Telecommunications Group, Incorporated
                    1700 Old Meadow Road
                    McLean, VA 22102
                    Attention: K. Paul Singh, Chairman, President and CEO
                    Facsimile:  (703) 902-2814"

      7. In the case of any inconsistency or conflict between the provisions of
this Amendment No. 1 and the provisions of the Voting Agreement, the provisions
of this Amendment No. 1 shall govern.

                                       6
<PAGE>
 
      8.   Except as expressly provided for in this Amendment No. 1, all terms,
conditions and obligations contained in the Voting Agreement are hereby
confirmed and shall remain unchanged and in full force and effect.

      9.   This Amendment No. 1 may be executed by facsimile signature which
shall be deemed to be an original for all purposes and may be executed in any
number of counterparts, each of which shall be deemed to be an original and all
of which, when taken together, shall constitute but one and the same instrument.

     10.   THIS AMENDMENT NO. 1 SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE
WITH THE LAWS OF THE STATE OF FLORIDA, WITHOUT REGARD TO SUCH STATE'S CONFLICTS
OF LAWS RULES.

                                       7
<PAGE>
 
          IN WITNESS WHEREOF, the Purchaser has caused this Amendment No. 1 to
be executed by its duly authorized officers, and the Shareholder has duly
executed this Amendment No. 1, each as of the date and year first above written.


                    PURCHASER:

                 PRIMUS TELECOMMUNICATIONS GROUP, INCORPORATED
 

                                                                    EXHIBIT 99.1
 
MCLEAN, Va., and FORT LAUDERDALE, Fla., April 17/PRNewswire/--Primus
Telecommunications Group, Incorporated (Nasdaq: PRTL) and TresCom International,
                                                ----
Inc. (Nasdaq: TRES) jointly announced today that Primus has agreed to increase
              ----
the consideration payable to TresCom shareholders in the pending merger between
Primus and TresCom in exchange for options granted by certain TresCom
shareholders that would enable Primus to acquire more than 50% of the
outstanding shares of TresCom common stock in defined circumstances even if the
merger were not consummated. For so long as these options are exercisable,
Primus also has an irrevocable proxy to vote the shares with respect to matters
relating to the merger. Pursuant to the amended merger agreement, TresCom
shareholders would be entitled to receive $12 per TresCom share payable in
Primus common stock, instead of the prior $10 per TresCom share payable in
Primus common stock which was subject to potential downward adjustment.

The options were granted to Primus by Warburg, Pincus Investors, L.P. and
certain executive officers of TresCom to purchase all of their shares for $12
per share payable in Primus common stock, and are exercisable in the event that
the merger agreement is terminated under defined circumstances. In the event
Primus were to exercise the option granted by Warburg, Pincus Investors, L.P.,
Primus would also be required to offer to purchase all of the outstanding shares
of TresCom common stock from TresCom's other shareholders at $12 per share
payable in Primus common stock.

K. Paul Singh, Chairman, President and CEO of Primus, stated "Our number one
priority is to complete our strategic merger with TresCom. We are enthusiastic
about the revised agreement as it brings increased certainty to achieving that
goal. By providing Primus entry into the Caribbean and Latin American markets we
will have a presence in every major region of the world, making Primus the
carrier with the broadest geographic coverage among our peer group. This
acquisition will propel Primus to the number 1 spot in terms of total revenue
among publicly held emerging global telecommunications carriers. We are well
advanced in securing the necessary regulatory approvals for the transaction, and
the enhanced certainty allows us to proceed with the execution of our strategy
for expansion into Latin America."

"TresCom's customer base, network facilities and marketing programs complement
Primus and we are eager to implement the combined strategies for the Latin
American market," stated Wesley T. O'Brien, Chief Executive Officer and
President of TresCom.

"Warburg, Pincus is delighted at the prospect of becoming a core shareholder of
Primus and looks forward to a long-term relationship. Our actions evidence our
belief in Primus' management and its global strategy," commented Douglas Karp,
Managing Director of E.M. Warburg, Pincus & Co., LLC.

Primus Telecommunications Group, Incorporated is a global telecommunications 
company providing domestic and international long-distance voice, data, private 
network and value-added services. Founded in 1994 and based in McLean, Va., 
Primus now serves 175,000 corporate, small- and medium-sized business, 
residential and wholesale customers located in North America, Europe and 
Asia-Pacific. News and information are available at the company's Website at 
http://www.primustel.com.
- ------------------------

TresCom is a facilities-based international telecommunications company with 
headquarters in Fort Lauderdale, Florida. The Company specializes in Caribbean 
and Latin American markets and offers a broad array of competitively priced 
services, including international and domestic long distance, travel and 
prepaid calling cards, and specialized international products and services. 
TresCom provides long-distance service to more than 230 countries and 
territories worldwide through its international network.

Certain statement contained in this press release which express "belief,"
"anticipation," "expectation" or "intention" and statements regarding the
consummation of the proposed merger, insofar as they may apply prospectively and
are not historical facts, are "forward-looking" statements within the meaning of
Section 27A of the Securities Act of 1933, as amended, and Section 21E of the
Securities and Exchange Act of 1934, as amended. Because such statements include
risks and uncertainties, actual results may differ materially from those
expressed or implied by such forward-looking statements.

SOURCE Primus Telecommunications Group, Incorporated

CONTACT: Neil L. Hazard of Primus Telecommunications Group, 703-902-2815; or 
Angie Spoto of TresCom, 954-713-1567; or General, Jeff Bogart; Investors, Jordan
Darrow; or Media, Alicia-Nieva Woodgate, 212-661-8030, all of The Financial
Relations Board Quote for referenced ticker symbols: TRES, PRTL
                                                     ----  ----
(C)1998, PR Newswire


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