ASSIGNMENT AND ASSUMPTION AGREEMENT
                                  AND RELEASE


     This Assignment and Assumption Agreement and Release (this "Agreement") is
made as of October 2, 1998 by and among CAIS, Inc., a Virginia corporation,
Cleartel Communications, Inc., a District of Columbia corporation (together
referred to as "Assignors"), CGX Communications, Inc., a Delaware corporation
("Assignee"), and William M. Caldwell, IV ("Employee").

                                   RECITALS:
                                   -------- 

     1.   Assignors are party to a certain employment agreement (the "Employment
          Agreement") dated as of September 8, 1997 between Assignors and
          Employee.

     2.   Pursuant to the Employment Agreement, Assignors granted to Employee
          certain options to purchase limited partnership interests in CAIS
          Limited Partnership and Cleartel Communications Limited Partnership
          (the "Partnerships"), or, in the event that the Partnerships are
          merged into Assignee, options to purchase shares of Assignee (the
          "Options"). In addition, Assignors separately agreed to grant Employee
          a limited partnership interest in CAIS Limited Partnership.

     3.   Simultaneously herewith, Assignors and Assignee are consummating
          certain transactions whereby Assignors will become wholly owned
          subsidiaries of Assignee (the "Restructuring").

     4.   In connection with the Restructuring, Assignors desire to assign all
          of their rights and obligations under the Employment Agreement to
          Assignee, and Assignee desires to assume all of Assignors' rights and
          obligations under the Employment Agreement, subject to and in
          accordance with the terms and conditions set forth in this Agreement.

     6.   Employee desires to release Assignors from their performance under the
          Options, and to release Assignors and CAIS Limited Partnership from
          any obligation to grant Employee a limited partnership interest in
          CAIS Limited Partnership, subject to his receipt of new options from
          Assignee and further subject to and in accordance with the terms and
          conditions set forth in this Agreement.

     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows.

     1.   Assignors hereby assign all of their rights and obligations under the
Employment Agreement to Assignee, and Assignee hereby accepts such assignment
and agrees to perform each and every obligation and covenant of Assignors
related to the Employment Agreement.
<PAGE>
 
     2.   Assignee hereby grants to Employee new options to purchase 1,634,610
          shares of the common stock, par value $.01 per share, of Assignee for
          a purchase price of $0.9732 per share, which options shall be subject
          to all of the terms and conditions applicable to the Options set forth
          in Exhibit A to the Employment Agreement.

     3.   Assignee hereby grants to Employee new options to purchase 97,465
          shares of the common stock, par value $.01 per share, of Assignee for
          a purchase price of $0.9732 per share.

     4.   Employee hereby releases and discharges Assignors and the Partnerships
          from any and all duties, liabilities, claims and performance under the
          Options, and relinquishes any further claim or entitlement to any
          additional equity interest in Assignors, Assignee and the Partnerships
          arising by virtue of the Employment Agreement or any other agreement,
          whether verbal or in writing, existing as of the date hereof between
          Employee and any of Assignors, Assignee or the Partnerships, except
          for the entitlement of the Employee to receive new options as provided
          in paragraphs 2 and 3 above.

     5.   Employee hereby consents to the assignment of the Employment Contract
          from Assignors to Assignee.

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the date first written above.

                   [SIGNATURES APPEAR ON THE FOLLOWING PAGE]
<PAGE>
 
                              ASSIGNORS:

                              CAIS, INC.


                              By: /s/ Ulysses G. Auger, II
                                  ------------------------
                              Ulysses G. Auger, II, President

                              CLEARTEL COMMUNICATIONS, INC.


                              By: /s/ Ulysses G. Auger, II
                                  ------------------------
                              Ulysses G. Auger, II, President

                              ASSIGNEE:

                              CGX COMMUNICATIONS, INC.


                              By: /s/ Ulysses G. Auger, II
                                  ------------------------
                              Ulysses G. Auger, II, President


                              EMPLOYEE:


                              /s/ William M. Caldwell, IV
                              ---------------------------
                              William M. Caldwell, IV

 

Source: OneCLE Business Contracts.