1 Exhibit 2.4 THIRD AMENDMENT TO AGREEMENT AND PLAN OF MERGER This Third Amendment to Agreement and Plan of Merger ("Amendment") is entered into as of May 10, 2000 by and among AT&T Corp. ("Parent"), a New York corporation, AT&T Latin America Corp....

   1
                                                                    Exhibit 2.4


                THIRD AMENDMENT TO AGREEMENT AND PLAN OF MERGER

     This Third Amendment to Agreement and Plan of Merger ("Amendment") is
entered into as of May 10, 2000 by and among AT&T Corp. ("Parent"), a New York
corporation, AT&T Latin America Corp. ("RV"), a Delaware corporation (formerly
named Kiri Inc.), Frantis, Inc. ("Merger Sub"), a Delaware corporation, and
FirstCom Corporation (the "Company"), a Texas Corporation.

                                    RECITALS

     A. Parent, RV, Merger Sub and the Company (the "Parties") have entered into
an Agreement and Plan of Merger, dated as of November 1, 1999 (as amended, the
"Merger Agreement"). Capitalized terms used herein without definition have the
meaning given them in the Merger Agreement.

     B. The Parties amended the Merger Agreement on February 1, 2000 to extend
the date on which either of them may terminate the Merger Agreement from April
30, 2000 to May 31, 2000.

     C. The Parties desire to extend further again the date on which Parent or
the Company may terminate the Merger Agreement.

     NOW, THEREFORE, the parties agree as follows:

          1. DEFINED TERMS.  Capitalized terms used herein without definition
     shall have the respective meanings ascribed to them in the Merger
     Agreement.

          2. EXTENSION OF DATE.  The date of May 31, 2000 appearing in clause
     (i) of Section 6.1(b) of the Merger Agreement is hereby amended to read
     "June 30, 2000."

          3. NO OTHER AMENDMENT OR MODIFICATION.  The Merger Agreement shall
     remain in full force and effect except as expressly amended or modified
     hereby.

          4. COUNTERPARTS.  This Amendment may be executed by one or more of the
     parties hereto on any number of separate counterparts, and all of such
     counterparts taken together shall be deemed to constitute one and the same
     instrument.

          5. EFFECTIVENESS.  This Amendment shall be effective only upon
     execution and delivery by each of the parties hereto.

               [INTENTIONALLY LEFT BLANK; SIGNATURE PAGE FOLLOWS]
   2

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed as of the date first written above.

                                          AT&T Corp.

                                          By: /s/ XXXX X. XXXXX
                                          --------------------------------------
                                          Name: Xxxx X. Xxxxx
                                          Title: Vice President

                                          AT&T Latin America Corp.

                                          By: /s/ XXXX X. XXXXX
                                          --------------------------------------
                                          Name: Xxxx X. Xxxxx
                                          Title: President

                                          Frantis, Inc.

                                          By: /s/ XXXX XXXXXXX
                                          --------------------------------------
                                          Name: Xxxx Xxxxxxx
                                          Title: Secretary

                                          FirstCom Corporation

                                          By: /s/ XXXXXXXX X. NORTHLAND
                                          --------------------------------------
                                          Name: Xxxxxxxx X. Northland
                                          Title: President and Chief Executive
                                          Officer