<PAGE>


                                   [ATI LOGO]

                        ADVANCED TELECOMMUNICATIONS, INC.

                              ISSUANCE AND SALE OF
                            SERIES Cl PREFERRED STOCK

                                DECEMBER 13, 1999



<PAGE>


                                 AMENDMENT NO. 1

                                       TO

                   SERIES C PREFERRED STOCK PURCHASE AGREEMENT

     This Amendment No. 1 to Series C Preferred Stock Purchase Agreement (the
"AMENDMENT") is made as of December 13, 1999 by and among:

     (i)    Advanced Telecommunications, Inc., a Delaware corporation (the
            "Company");

     (ii)   Stolberg, Meehan & Scano II, L.P. ("Stolberg");

     (iii)  Bain Capital Fund VI, L.P. ("Bain") and the other Persons who are
            listed on the signature pages hereto as Bain Purchasers (the "BAIN
            PURCHASERS");

     (iv)   J.P. Morgan Ventures Corporation ("JP Morgan");

     (v)    Mount Washington Associates L.L.C. ("MOUNT WASHINGTON");

     (vi)   Steven M. Simon ("Simon");

     (vii)  Paul Cady ("P._Cady");

     (viii) Daniel P. Cady and Jane Maland Cady ("D. Cady"); and

     (ix)   David G. Cady and Kim S. Cady ("DG Cady").

                                    RECITALS

     1. The Bain Purchasers, Stolberg, JP Morgan, Mount Washington, Simon, P.
Cady, D. Cady and DG Cady (collectively, the "SUBSEQUENT PURCHASERS") have
agreed to purchase shares of the Company's Series Cl Preferred Stock, par value
$0.01 per share (the "SERIES Cl PREFERRED STOCK") on the conditions and subject
to the terms set forth in the Series C Preferred Stock Purchase Agreement dated
September 30, 1999 by and among the Company, the Bain Purchasers, Stolberg and
certain other Purchasers (the "STOCK PURCHASE AGREEMENT"), as amended by this
Amendment.

     2. The Company and the Majority Purchasers, which includes the Majority
Bain Purchasers and Stolberg, desire to amend the Stock Purchase Agreement to
include JP Morgan, Mount Washington, Simon, P. Cady, D. Cady and DG Cady as
parties thereto and to include the Series Cl Preferred Stock as Shares
thereunder. Capitalized terms used herein and not otherwise defined herein shall
have the meanings ascribed to them in the Stock Purchase Agreement.


<PAGE>


                                    AGREEMENT


     Therefore, the parties hereto hereby agree as follows:

     1. All references in the Stock Purchase Agreement and this Amendment to the
"STOCK PURCHASE AGREEMENT" or the "AGREEMENT" shall be deemed to mean the Stock
Purchase Agreement, as amended by this Amendment.

     2. The defined term "SHARES" in the Stock Purchase Agreement shall be
deemed to include the shares of Series Cl Preferred Stock sold to the Subsequent
Purchasers pursuant to the Stock Purchase Agreement.

     3. The defined term "STOCKHOLDERS AGREEMENT" shall be deemed to mean the
Stockholders Agreement, as amended by Amendment No. 1 to Amended and Restated
Stockholders Agreement dated as of the date hereof by and among the Company, the
Bain Purchasers, Stolberg and certain other stockholders of the Company (the
"AMENDMENT TO STOCKHOLDERS AGREEMENT").

     4. Section 1.3 of the Stock Purchase Agreement is hereby amended by
replacing it in its entirety with the following:

          "1.3. SALE OF SHARES AT SUBSEQUENT CLOSINGS.

               1.3.1 SALE OF SHARES AT FIRST SUBSEQUENT CLOSING. The Company
          shall adopt and file with the Secretary of State of Delaware on or
          prior to the closing of the purchase of Series Cl Preferred Stock
          hereunder on December 13, 1999 (the "FIRST SUBSEQUENT CLOSING") a
          Second Amended and Restated Certificate of Incorporation in the form
          attached hereto as EXHIBIT L (the "SECOND AMENDED CHARTER").
          Subject to the terms and conditions contained herein, and based on the
          representations and warranties contained herein, each Subsequent
          Purchaser agrees, severally, to purchase, and the Company agrees to
          issue and sell to each Subsequent Purchaser on January 4, 2000, that
          number of shares of Series Cl Preferred Stock set forth in the column
          First Subsequent Closing opposite each Subsequent Purchaser's name on
          EXHIBIT A hereto at the per share purchase price of $6.00 (the "FIRST
          SUBSEQUENT PURCHASE PRICE").

               1.3.2 SALE OF SHARES AT OTHER SUBSEQUENT CLOSINGS. Subject to all
          of the terms and conditions of this Agreement and based on the
          representations and warranties contained herein, at any time after
          March 31, 2000 and prior to September 30, 2001, at the option of the
          Company and upon not less than ten Business Days prior written notice
          to the Bain Purchasers, the Bain Purchasers will purchase at not more
          than three subsequent closings (each, together with the First
          Subsequent Closing, a "SUBSEQUENT CLOSING") at a per share purchase
          price of $5.00 (or such other per share purchase price


                                      -2-
<PAGE>


          as shall be agreed to in writing by the Majority Bain Purchasers and a
          majority of the disinterested members of the Company's board of
          directors) a number of Shares not exceeding 6,000,000 shares; PROVIDED
          that in addition to the conditions set forth in Section 4.4 hereof,
          the following conditions have been met: (a) the Company shall have
          achieved the operational and financial targets set forth on EXHIBIT C
          hereto and (b) the CLEC Basket Market Value shall be greater than
          11.2, as calculated on EXHIBIT D hereto (the "BASE MARKET VALUE");
          PROVIDED, HOWEVER that in the event that one or more of the Designated
          CLECs ceases to be a publicly traded company trading under the ticker
          symbol under which it is trading as of Initial Closing, the Base
          Market Value shall be recalculated in good faith to exclude such
          Designated CLEC from the calculation."

     5. Section 4.4 of the Stock Purchase Agreement is hereby amended by
renumbering it as Section 4.5.

     6. Section 4.3 of the Stock Purchase Agreement is hereby amended by
replacing it in its entirety with the following:

               "4.3. FIRST SUBSEQUENT CLOSING. The obligations of each of the
          Subsequent Purchasers under Section 1 of this Agreement to purchase
          Shares at the First Subsequent Closing are subject to the fulfillment
          on or before the First Subsequent Closing of each of the following
          conditions unless waived in accordance with Section 8.1:

                    4.3.1. REPRESENTATIONS AND WARRANTIES. The representations
               and warranties of the Company contained in Section 2, as amended
               by the amended Schedules attached hereto as EXHIBIT M (the
               "AMENDED SCHEDULES"), shall be true and correct in all material
               respects on and as of the date of the First Subsequent Closing
               with the same effect as though such representations and
               warranties had been made on and as of the date of such First
               Subsequent Closing and the Subsequent Purchasers shall have
               received a certificate of the Chief Executive Officer or Chief
               Operating Officer of the Company to that effect.

                    4.3.2 PERFORMANCE. The Company shall have performed and
               complied with all agreements, obligations, and conditions
               contained in this Agreement and the Stockholders Agreement that
               are required to be performed or complied with by it on or before
               the First Subsequent Closing.

                    4.3.3 BOARD DETERMINATIONS. The board of directors of the
               Company shall have approved all issuances of Shares at the First
               Subsequent Closing and determined that the financing to be
               provided by the issuance and sale of Shares at the First
               Subsequent Closing is necessary or desirable in connection with
               the funding of the business of the Company and its Subsidiaries.


                                      -3-
<PAGE>


                    4.3.4 FILING OF SECOND AMENDED CHARTER. The Company shall
               have filed with the Secretary of State of Delaware the Second
               Amended Charter in the form attached hereto as EXHIBIT L and the
               Second Amended Charter shall have become effective.

                    4.3.5 OUALIFICATIONS. All authorizations, approvals, or
               permits, if any, of any governmental authority or regulatory body
               of the United States or of any state that are required in
               connection with the lawful issuance and sale of Shares to the
               Subsequent Purchasers or the execution, delivery and performance
               by the Company of this Agreement and the Stockholders Agreement
               shall have been duly obtained and shall be effective on and as of
               the First Subsequent Closing, other than those which are not
               required to be obtained before the First Subsequent Closing.

                    4.3.6 AMENDMENT TO STOCKHOLDERS AGREEMENT. The Amendment to
               Stockholders Agreement in the form attached hereto as EXHIBIT N
               shall have been executed and delivered by the parties thereto
               (other than the Purchasers in their capacity as such), no such
               party shall be in breach or default thereof and the Amendment to
               Stockholders Agreement shall be in full force and effect as of
               the First Subsequent Closing.

                    4.3.7 CONTINUED FULFILLMENT. The conditions set forth in
               Sections 4.1.4, 4.1.5 and 4.1.6 shall continue to have been
               fulfilled at the First Subsequent Closing.

                    4.3.8 SECRETARY'S CERTIFICATE. The Secretary of the Company
               shall have delivered to the Subsequent Purchasers at the First
               Subsequent Closing a Certificate dated as of the First Subsequent
               Closing, certifying: (a) that attached thereto is a true and
               complete copy of the by-laws of the Company as in effect on the
               date of such certification; (b) that attached thereto is a true
               and complete copy of all resolutions adopted by the board of
               directors of the Company authorizing the execution, delivery and
               performance of this Amendment and the Amendment to Stockholders
               Agreement and the issuance, sale and delivery of the Shares, and
               that all such resolutions are in full force and effect and are
               all the resolutions adopted in connection with the transactions
               contemplated by this Agreement and the Stockholders Agreement;
               (c) that attached thereto is a true and complete copy of the
               charter of the Company as amended by the Second Amended Charter
               and (d) to the incumbency and specimen signature of certain
               officers of the Company.

                    4.3.9 OPINION OF COMPANY COUNSEL. The Subsequent Purchasers
               shall have received from Piper Marbury Rudnick & Wolfe LLP,
               counsel for the Company, an opinion substantially in the form
               (including, with respect to the Second Amended Charter, paragraph
               3) attached hereto as EXHIBIT G.


                                      -4-

<PAGE>


                    4.3.10 THIRD PARTY CONSENTS. The Company and each Subsidiary
               shall have received all required third party consents necessary
               to the consummation of the transactions contemplated by this
               Agreement.

                    4.3.11 PROCEEDINGS AND DOCUMENTS. All instruments and legal,
               governmental, administrative, corporate and partnership
               proceedings in connection with the issuance of Shares, this
               Agreement and the Amendment to Stockholders Agreement shall be
               reasonably satisfactory in form and substance to the Subsequent
               Purchasers, and the Subsequent Purchasers shall have received
               copies of all documents, including, without limitation, records
               of corporate or other proceedings, and any consents, licenses,
               approvals, permits and orders required to be secured by the
               Company in connection with the issuance of Shares, this Agreement
               and the Amendment to Stockholders Agreement or which any
               Purchaser may have reasonably requested in connection therewith.

               4.4. OTHER SUBSEQUENT CLOSINGS. The obligations of each of the
          Bain Purchasers under Section 1 of this Agreement to purchase Shares
          at each Subsequent Closing other than the First Subsequent Closing are
          subject to the fulfillment on or before each such Subsequent Closing
          of each of the following conditions unless waived in accordance with
          Section 8.1:

                    4.4.1. REPRESENTATIONS AND WARRANTIES. The representations
               and warranties of the Company contained in Section 2 shall be
               true and correct in all material respects on and as of the date
               of each Subsequent Closing with the same effect as though such
               representations and warranties had been made on and as of the
               date of such Subsequent Closing and the Bain Purchasers shall
               have received a certificate of the Chief Executive Officer or
               Chief Operating Officer of the Company to that effect.

                    4.4.2 PERFORMANCE. The Company shall have performed and
               complied with all agreements, obligations, and conditions
               contained in this Agreement and the Stockholders Agreement that
               are required to be performed or complied with by it on or before
               such Subsequent Closing.

                    4.4.3 BOARD DETERMINATIONS. The board of directors of the
               Company shall have approved all issuances of Shares at such
               Subsequent Closing and determined that the financing to be
               provided by the issuance and sale of Shares at such Subsequent
               Closing is necessary or desirable in connection with the funding
               of the business of the Company and its Subsidiaries.

                    4.4.4 CONTINUED FULFILLMENT. The conditions set forth in
               Sections 4.1.4, 4.1.5 and 4.1.6 shall continue to have been
               fulfilled at each such Subsequent Closing.

                                      -5-


<PAGE>


                    4.4.5 SECRETARY'S CERTIFICATE. The Secretary of the Company
               shall have delivered to the Bain Purchasers at such Subsequent
               Closing a Certificate, dated as of such Subsequent Closing,
               certifying: (a) that attached thereto is a true and complete copy
               of the by-laws of the Company as in effect on the date of such
               certification; (b) that attached thereto is a true and complete
               copy of all resolutions adopted by the board of directors of the
               Company authorizing the issuance, sale and delivery of the
               Shares, and that all such resolutions are in full force and
               effect and are all the resolutions adopted in connection with the
               transactions contemplated by this Agreement and the Stockholders
               Agreement; (c) that attached thereto is a true and complete copy
               of the charter of the Company as amended by the Second Amended
               Charter and (d) to the incumbency and specimen signature of
               certain officers of the Company.

                    4.4.6 OUALIFICATIONS. All authorizations, approvals, or
               permits, if any, of any governmental authority or regulatory body
               of the United States or of any state that are required in
               connection with the lawful issuance and sale of Shares to the
               Bain Purchasers or the execution, delivery and performance by the
               Company of this Agreement and the Stockholders Agreement shall
               have been duly obtained and shall be effective on and as of each
               Subsequent Closing, other than those which are not required to be
               obtained before each Subsequent Closing.

                    4.4.7 OPINION OF COMPANY COUNSEL. The Purchasers shall have
               received from Piper Marbury Rudnick & Wolfe LLP, counsel for the
               Company, an opinion substantially in the form (other than
               paragraph 3) attached hereto as EXHIBIT C.

                    4.4.8 THIRD PARTY CONSENTS. The Company and each Subsidiary
               shall have received all required third party consents necessary
               to the consummation of the transactions contemplated by this
               Agreement.

                    4.4.9 PROCEEDINGS AND DOCUMENTS. All instruments and legal,
               governmental, administrative, corporate and partnership
               proceedings in connection with the issuance of Shares, this
               Agreement and the Stockholders Agreement shall be reasonably
               satisfactory in form and substance to the Bain Purchasers, and
               the Bain Purchasers shall have received copies of all documents,
               including, without limitation, records of corporate or other
               proceedings, and any consents, licenses, approvals, permits and
               orders required to be secured by the Company in connection with
               the issuance of Shares, this Agreement and the Stockholders
               Agreement or which any Purchaser may have reasonably requested in
               connection therewith."

     7. Section 6.3 of the Stock Purchase Agreement is hereby amended by
replacing it in its entirety with the following:


                                      -6-
<PAGE>


          "OTHER PURCHASERS" shall mean BancBoston Robertson Stephens Inc.,
     Bayview 99 I, L.P., Bayview 99 II, L.P., Clark Callander, Richard
     Innenberg, JP Morgan, Mount Washington, Simon, P. Cady, D. Cady and DG
     Cady."

     8. Each of JP Morgan, Mount Washington, Simon, P. Cady, D. Cady and DG Cady
shall become a party to the Stock Purchase Agreement by its execution of the
signature page hereto and shall be designated as a "Purchaser" thereunder.

     9. EXHIBIT A to the Stock Purchase Agreement is hereby amended by replacing
it in its entirety with EXHIBIT A attached hereto.

     10. The parties hereto acknowledge that Susan E. Rivera and Thomas J.
Rivera ("RIVERA") have preemptive rights under the Stockholders Agreement in
connection with the issuance of Shares at the First Subsequent Closing which
they have not exercised to date. The number of shares of Series Cl Preferred
Stock authorized in the Second Amended Charter shall be sufficient to
accommodate the issuance of Shares to Rivera in the event Rivera exercises its
preemptive rights. In the event that Rivera exercises its preemptive rights to
purchase shares of Series Cl Preferred Stock, the parties agree that Rivera may
become a party to the Stock Purchase Agreement by executing a joinder agreement
and upon execution of such joinder agreement shall be designated as a
"Purchaser" under the Stock Purchase Agreement entitled to rights and subject to
obligations applicable to a Purchaser thereunder.

     11. Except as specifically amended by this Amendment, the Stock Purchase
Agreement shall remain in full force and effect in accordance with its terms.

     12. This Amendment may be executed in any number of counterparts, each of
which shall constitute an original, but all of which, taken together, shall
constitute one and the same agreement.


                                      -7-
<PAGE>


     IN WITNESS WHEREOF, each of the undersigned has duly executed this
Amendment as of the date first written above.

THE COMPANY:              ADVANCED TELECOMMUNICATIONS, INC.


                          By: /s/ Clifford D. Williams
                              -----------------------------------------
                              Clifford D. Williams,
                              Chief Executive Officer



<PAGE>


BAIN PURCHASERS:                   BAIN CAPITAL FUND VI, L.P.
                                   By: Bain Capital Partners VI, L.P.,
                                         its general partner
                                   By: Bain Capital Investors VI, Inc.,
                                         its general partner

                                   By:  /s/  Michael A. Krupka
                                       -----------------------------------
                                   Name:   Michael A. Krupka
                                   Title: Managing Director

                                   BCIP ASSOCIATES II
                                   BCIP TRUST ASSOCIATES II
                                   BCIP ASSOCIATES II-B
                                   BCIP TRUST ASSOCIATES II-B
                                   BCIP ASSOCIATES II-C
                                   By: Bain Capital, Inc.,
                                         their Managing Partner

                                   PEP INVESTMENTS PTY LTD.
                                   By: Bain Capital, Inc.,
                                         its attorney-in-fact

                                   By:  /s/  Michael A. Krupka
                                       ------------------------------------
                                   Name:   Michael A. Krupka
                                   Title: Managing Director

                                   SANKATY HIGH YIELD ASSET PARTNERS, L.P.
                                   By  /s/ Jonathan S. Levine
                                       ------------------------------------
                                   Name:  Jonathan S. Levine
                                   Title: Managing Director

                                   RGTP, LLC

                                   By:_____________________________________
                                   Name:
                                   Title:


<PAGE>

BAIN PURCHASERS:                   BAIN CAPITAL FUND VI, L.P.
                                   By:  Bain Capital Partners VI, L.P.,
                                           its general partner
                                   By:  Bain Capital Investors VI, Inc.,
                                           its general partner
                                   By:______________________________________
                                   Name:   Michael A. Krupka
                                   Title: Managing Director

                                   BCIP ASSOCIATES II
                                   BCIP TRUST ASSOCIATES II
                                   BCIP ASSOCIATES II-B
                                   BCIP TRUST ASSOCIATES II-B
                                   BCIP ASSOCIATES II-C
                                   By: Bain Capital, Inc.,
                                         their Managing Partner

                                   PEP INVESTMENTS PTY LTD.
                                   By: Bain Capital, Inc.,
                                         its attorney-in-fact

                                   By:_______________________________________
                                   Name:   Michael A. Krupka
                                   Title: Managing Director

                                   SANKATY HIGH YIELD ASSET PARTNERS, L.P.

                                   By _______________________________________
                                      Name:
                                      Title: Managing Director

                                   RGIP, LLC

                                   By: /s/ R. Bradford Malt
                                       --------------------------------------
                                   Name: R. Bradford Malt
                                   Title: Managing Member


<PAGE>


STOLBERG:                          STOLBERG MEEHAN & SCANO II, L.P.
                                   A DELAWARE LIMITED PARTNERSHIP
                                   BY: STOLBERG MEEHAN & SCANO LLC,
                                       GENERAL PARTNER


                                   By: /s/
                                      ----------------------------------------
                                   Name:
                                   Title:




<PAGE>



JP MORGAN:                         J.P. MORGAN VENTURES CORPORATION


                                   By: /s/ John A. Mayer
                                      ----------------------------------------
                                   Name: John A. Mayer
                                   Title: Director


<PAGE>



MOUNT WASHINGTON:                  MOUNT WASHINGTON ASSOCIATES L.L.C.

                                   By: /s/ Edwin M. Martin, Jr.
                                      ----------------------------------------
                                   Name: Edwin M. Martin, Jr.
                                   Title: Managing Member



<PAGE>



SIMON:                             /s/ Steven M. Simon
                                   -------------------------------------------
                                   Steven M. Simon



<PAGE>


CADY:                              /s/ Paul Cady
                                   -------------------------------------------
                                   Paul Cady


<PAGE>


DG CADY:                           /s/  David G. Cady & Kim S. Cady
                                   -------------------------------------------
                                   David G. Cady & Kim S. Cady,
                                   as Joint Tenants


<PAGE>


D. CADY:                           /s/  Daniel P. Cady & Jane Maland Cady
                                   -------------------------------------------
                                   Daniel P. Cady & Jane Maland Cady,
                                   as Joint Tenants