1
                                                                     Exhibit 2.2


            FORM OF AMENDMENT AGREEMENT TO SHAREHOLDER'S UNDERTAKING

This AMENDMENT AGREEMENT dated as of ___ October 1998 (as amended or modified
from time to time in accordance with the terms hereof, this "Amendment
Agreement") is by and between ________________ ("Seller"), and Global
TeleSystems Group, Inc., a Delaware, USA, corporation, or such affiliate thereof
which may be designated thereby (Global TeleSystems Group, Inc. or such
designated affiliate thereof hereinafter referred to as "Offeror").

WHEREAS

Seller is a shareholder of NetSource Europe ASA ("NetSource Europe"), a
Norwegian corporation;

Offeror intends to make an offer to NetSource Europe's shareholders to acquire
from them the capital stock of NetSource Europe and therefore wishes to purchase
from Seller the NetSource Europe Shares (as defined in the Shareholder's
Undertaking (as defined herein)) on the terms set forth herein;

Offeror and certain shareholders of NetSource Europe owning or controlling an
aggregate number of shares in NetSource Europe exceeding 50 per cent of the
issued share capital of NetSource Europe ("the Accepting Shareholders"), a list
of which is attached as Exhibit 1 (wich the parties hereto hereby acknowledge
may not be complete), have entered into Shareholder's Undertakings ("the
Shareholder's Undertakings", such shareholder's undertaking which has been
entered into between Offeror and Seller is hereinafter referred to as the
"Seller Shareholder's Undertaking") under the terms of which Offeror, subject to
certain conditions has agreed to make an offer to acquire the whole of the share
capital of NetSource Europe by 16 October 1998; and

Offeror and Seller have agreed on revised terms of the Offer (as defined in the
Shareholder's Undertakings).

NOW, THEREFORE, in consideration of the representations, warranties, covenants
and agreements hereinafter set forth, the parties hereto hereby agree as
follows:

1.       The Offer shall be open for acceptance by NetSource Europe's
         shareholders until 30 October 1998 3 p.m. CET, inclusive.

2.       In the event that the fully diluted number of shares in the capital of
         NetSource Europe is reduced from the current number of 29,379,688
         shares by the waiver of options or other rights to require issued
         shares in NetSource Europe not later than 3 days before the Settlement
         Date, the consideration offered per share in NetSource Europe shall be
         adjusted upwards accordingly.

3.       The criteria for any additional payment set forth in clause 3 of the
         Term Sheet shall be amended as follows:

                (i)   The criteria shall be understood as based on International
         Accounting Standards; 

                (ii)  the criterion "Cumulative Consolidated Net Revenue" shall 
         be Cumulative Consolidated Gross Revenue; and

                (iii) no conversion of the criteria to United States generally
         accepted accounting principles shall take place.








   2


4.       All references in the Seller Shareholder's Undertaking to the "Offer"
         shall be understood as references to the Offer made on the terms set
         forth in the Seller Shareholder's Undertaking as amended hereby (the
         "Amended Offer Terms").

5.       This Amendment Agreement shall be conditional upon each of the
         Accepting Shareholders having entered into amendment agreements with
         Offeror, duly executed in writing and delivered by both parties, on
         terms identical to the terms hereof, except that Offeror may waive such
         condition unilaterally in which case, i.e., Seller shall accept an
         Offer made on the Amended Offer Terms.

6.       If any NetSource Europe shareholder other than those set forth in
         Exhibit 1 have signed or sign a Shareholder's Undertaking without
         Offeror's knowledge thereof at the date hereof, Offeror shall have full
         discretion (unless if having acted in bad faith) to accept that such
         signature has come to bind it by such Shareholder's Undertaking(s),
         with the effect that the condition to this Amendment Agreement shall be
         deemed not to have been satisfied, provided, however, that before
         accepting to be bound Offeror shall afford, by written notice
         containing necessary particulars, NetSource Europe opportunity for a
         period of 7 days to recommend such NetSource Europe shareholder to
         enter into an amendment agreement on the terms identical to the terms
         hereof and shall accept to be bound by the shareholder's agreement
         thereto. In the event that the shareholder in question in spite thereof
         does not agree to enter into such amendment agreement, Seller shall,
         for a period of 30 days from the time Seller has informed Offeror in
         writing of this fact, refrain from requiring under the terms of Article
         6 of the Shareholder's Undertaking (if still applicable) that Offeror
         make the Offer on the terms therein set forth.

7.       Provided that Offeror makes the Offer on the terms set forth in the
         Shareholder's Undertakings by the time set forth therein, the
         Termination Fee shall not be payable by Offeror in the event that
         Offeror fails to make the the Offer on the Amended Offer Terms, but
         this shall not exclude Seller from any other remedy available at law.


IN WITNESS WHEREOF, this Amendment Agreement has been duly executed on behalf of
the parties hereto by fax counterparts.


____ October  1998


Seller:                                                   Offeror:


- ---------------                                           --------------
By: Name:                                                 By: Name:
    Title:                                                    Title:




   3


List of Exhibits

Exhibit 1:   The Accepting Shareholders