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                                                                  EXHIBIT 3.15

                         CERTIFICATE OF AMENDMENT TO THE

                         CERTIFICATE OF INCORPORATION OF

                         GLOBAL TELESYSTEMS GROUP, INC.


         GLOBAL TELESYSTEMS GROUP, INC., a Delaware corporation, HEREBY
CERTIFIES AS FOLLOWS:

         1. The name of the Corporation is Global TeleSystems Group, Inc. The
date of filing of its Certificate of Incorporation with the Secretary of State
of the State of Delaware was September 30, 1993.

         2. This Certificate of Amendment sets forth amendments to the
Certificate of Incorporation of the Corporation that were duly adopted by the
holders of a majority of the outstanding stock of the Corporation entitled to
vote thereon in accordance with the provisions of Section 242 of the General
Corporation Law of the State of Delaware, at a meeting of stockholders duly
called and held, upon notice in accordance with the provisions of Section 222 of
the General Corporation Law of the State of Delaware.

         3. Article FIRST of the Certificate of Incorporation of the Corporation
is hereby amended in full to be and read as follows:

         "FIRST: The name of the corporation is Global TeleSystems, Inc. (the
`Corporation')."

         4. The first paragraph of Article FOURTH of the Certificate of
Incorporation of the Corporation is hereby amended to be and read as follows:

         "FOURTH: The total number of shares of capital stock which the
         Corporation shall have authority to issue is 550,000,000 (five hundred
         and fifty million) shares, of which there shall be 540,000,000 (five
         hundred and forty million) shares of common stock, par value $0.10 per
         share, and 10,000,000 (ten million) shares of preferred stock, par
         value $0.0001 per share."

         IN WITNESS WHEREOF, GLOBAL TELESYSTEMS GROUP, INC. has caused this
certificate to be signed by Grier C. Raclin, its Senior Vice President, External
Affairs; General Counsel and Corporate Secretary, and attested by Arnold Y.
Dean, its Vice President and Assistant Secretary, this 16th day of May, 2000.

                               GLOBAL TELESYSTEMS GROUP, INC.


                               By:
                                  ---------------------------------------------
                               Name:  Grier C. Raclin
                               Title: Senior Vice President, External Affairs;
                                      General Counsel and Corporate Secretary


ATTEST:


- ---------------------------------------
Vice President, Deputy General Counsel,
and Assistant  Secretary