<PAGE>   1
                                                      AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 1

                                                                   (4/8/96 NPPA)

                       NETWORK PRODUCTS PURCHASE AGREEMENT

                               NUMBER MC-10/96-DM

Northern Telecom Inc., a Delaware corporation having offices at 2350 Lakeside
Blvd., Richardson, Texas 75083 ("Nortel") and MIDCOM Communications Inc., a
state of Washington corporation, having its principal offices and place of
business at MIDCOM Tower, Suite 1600, 1111 Third Avenue, Seattle Washington
98101 ("Buyer") agree as follows:

1.      SCOPE

        1.1     Certain terms used in this Agreement shall be defined as set
                forth in Exhibit A.

        1.2     The terms and conditions of this Agreement shall apply to the
                purchase by Buyer and the sale by Nortel of Equipment and
                Services and the licensing of Software furnished in connection
                with such Equipment. The terms and conditions contained in a
                Product Attachment shall modify and/or supplement the other
                terms and conditions of this Agreement, only with respect to the
                Product Line and Services described in the Product Attachment.

        1.3     All Products and Services obtained by Buyer pursuant to this
                Agreement shall be obtained by Buyer solely for initial use by
                Buyer in its internal business to provide services available
                through its networks, and not as stock in trade or inventory
                which is intended for resale by Buyer to any third party as new
                and unused material. All such Products shall be installed in the
                United States.

2.      TERM

        2.1     This Agreement shall be in effect during the period that any
                Product Attachment is in effect. Each Product Attachment shall
                be in effect during its Product Attachment Term. This Agreement
                or any part thereof may be terminated in accordance with the
                express provisions of this Agreement concerning termination or
                by written agreement of the parties.

        2.2     The termination of this Agreement or any part thereof shall
                not affect the obligations of either party thereunder which have
                not been fully performed with respect to any accepted Order,
                unless such Order is expressly terminated in accordance with
                this Agreement or by written agreement of the parties.




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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 2

3.      ORDERING

        All purchases pursuant to this Agreement shall be made by means of
        Orders issued from time to time by Buyer, and executed by a Vice
        President of Buyer, and accepted by Nortel in writing within fifteen
        (15) days. Otherwise, any such Order shall be deemed to be void. All
        Orders shall reference this Agreement and the applicable Product
        Attachment and shall be governed solely by the terms and conditions set
        forth herein as modified and/or supplemented pursuant to Section 1.2 by
        the terms and conditions of any applicable Product Attachments.

4.      PRICES

        4.1     The prices, charges, and fees applicable to Orders shall be set
                forth in the appropriate Product Attachments and may be revised
                in accordance with the provisions stated therein. Buyer shall 
                pay transportation charges, including insurance, in accordance 
                with the applicable Product Attachment.

        4.2     Until the total of all prices, charges and fees for Products and
                related Services furnished hereunder shall have been paid to
                Nortel, Buyer shall cooperate with Nortel in perfecting Nortel's
                purchase money security interest in such Products and Buyer
                shall promptly execute all documents and take all actions
                required by Nortel in connection therewith. Buyer shall not
                sell, lease or otherwise transfer such Products or any portion
                thereof or allow any liens or encumbrances to attach to such
                Products or any portion thereof prior to payment in full to
                Nortel of the total of all such prices, charges, and fees.

5.      TERMS OF PAYMENT

        5.1     The amounts payable for Products and/or Services shall be
                invoiced by Nortel to Buyer in accordance with the applicable
                Product Attachments. All amounts payable and properly invoiced
                pursuant to this Agreement shall be paid by Buyer to Nortel
                within thirty (30) days from the date of Nortel's invoice in
                accordance with the payment instructions contained in such
                invoice.

        5.2     Overdue payments, excluding those which are the subject of a
                good faith dispute, shall be subject to interest charges,
                calculated daily commencing on the 31st day after the date of
                the invoice, at one percent (1%) per month or such lesser rate
                as may be the maximum permissible rate under applicable law.



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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 3

6.      TAXES

        Buyer shall at Nortel's appropriate direction promptly reimburse Nortel,
        file an appropriate exemption certificate or notice of exemption, or pay
        directly to the applicable government or taxing authority all taxes and
        charges arising hereunder, including, without limitation, penalties and
        interest resulting from the actions or failure to act by Buyer, except
        for taxes computed upon the net income of Nortel. The provisions of this
        Section 6 shall survive any termination of this Agreement.

7.      RISK OF LOSS, TITLE

        7.1     Risk of loss or damage to Products shall pass to Buyer upon
                delivery to the loading dock at the installation site or other
                delivery location specified by Buyer in its Order, and Buyer
                shall keep such Products fully insured for the total amount then
                due Nortel for such Products.

        7.2     Good title to Equipment furnished hereunder which shall be free
                and clear of all liens and encumbrances shall vest in Buyer upon
                full payment by Buyer of the total prices, charges and fees
                payable by Buyer for such Equipment and any related Software or
                Services furnished by Nortel in connection with such Equipment.

        7.3     Buyer shall receive a license to use Software subject to the
                terms set forth in Exhibit B.

8.      TESTING, TURNOVER AND ACCEPTANCE

        8.1     If Nortel installs any Products furnished hereunder, the rights
                and obligations of the parties with respect to testing, turnover
                and acceptance of such Products shall be as set forth in the
                applicable Product Attachment.

        8.2     If Nortel does not install Products furnished hereunder, Nortel
                shall prior to delivery of the Products perform such factory
                tests as Nortel determines to be appropriate in order to confirm
                that such Products shall be in accordance with the applicable
                Specifications. Buyer shall be deemed to have accepted the
                Products upon completion of such tests.

        8.3     In the event that Buyer places Products into revenue-generating
                service, such Products shall be deemed to have been accepted by
                Buyer without limitation or restriction.


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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 4

9.      DISCLAIMERS OF WARRANTIES AND REMEDIES

        THE WARRANTIES AND REMEDIES SET FORTH IN EXHIBIT D AND IN ANY PRODUCT
        ATTACHMENT CONSTITUTE THE ONLY WARRANTIES OF NORTEL WITH RESPECT TO THE
        PRODUCTS AND SERVICES AND BUYER'S EXCLUSIVE REMEDIES IN THE EVENT SUCH
        WARRANTIES ARE BREACHED. THEY ARE IN LIEU OF ALL OTHER WARRANTIES,
        WRITTEN OR ORAL, STATUTORY, EXPRESS OR IMPLIED, INCLUDING, WITHOUT
        LIMITATION ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
        PURPOSE. NORTEL SHALL NOT BE LIABLE FOR ANY INCIDENTAL OR CONSEQUENTIAL
        DAMAGES OF ANY NATURE WHATSOEVER, BEFORE OR AFTER THE PLACING OF ANY
        PRODUCT INTO SERVICE.

10.     LIABILITY FOR PERSONAL INJURY, PROPERTY DAMAGE AND PATENT INFRINGEMENT

        10.1    A party hereto shall defend the other party against any suit,
                claim, or proceeding brought against the other party for direct
                damages due to personal injuries (including death) or damage to
                tangible property which allegedly result from the negligence or
                willful misconduct of the defending party in the performance of
                this Agreement. The defending party shall pay all litigation
                costs, reasonable attorney's fees, settlement payments and such
                direct damages awarded or resulting from any such suit, claim or
                proceeding.

        10.2    Nortel shall defend Buyer against any suit, claim or proceeding
                brought against Buyer alleging that any Products, excluding
                Vendor Items, furnished hereunder infringe any United States
                patent. Nortel shall pay all litigation costs, reasonable
                attorney's fees, settlement payments and any damages awarded or
                resulting from any such suit, claim or proceeding. With respect
                to Vendor Items, Nortel shall assign any rights with respect to
                infringement of U.S. patents granted to Nortel by the supplier
                of such Vendor Items to the extent of Nortel's right to do so.

        10.3    The party entitled to defense pursuant to Section 10.1 or 10.2
                shall promptly advise the party required to provide such defense
                of the applicable suit, claim, or proceeding and shall cooperate
                with such party in the defense or settlement thereof. The party
                required to provide such defense shall have sole control of the
                defense of the applicable suit, claim, or proceeding and of all
                negotiations for its settlement or compromise.

        10.4    If an injunction is obtained against Buyer's use of any Products
                as a result of any suit, claim, or proceeding described in
                Section 10.2, Nortel shall at Nortel's option either:



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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 5

                10.4.1  promptly procure for Buyer the right to continue using
                        the portions of the Products enjoined from use; or

                10.4.2  promptly replace or modify the same with equivalent or
                        better Products so that Buyer's use is not subject to
                        any such injunction.

        10.5    If Nortel cannot perform under Section 10.4.1 or 10-4.2, Buyer
                shall have the right to return the infringing Products to Nortel
                upon written notice to Nortel, and in the event of such return,
                neither party shall have any further liabilities or obligations
                under this Agreement on account of such infringement or return,
                except Nortel shall refund the full price of the Products
                ordered during the period defined as twenty-four (24) months
                from the in service date of the Products and thereafter the
                depreciated value of such Products carried on Buyer's books at
                the time of such return, less any outstanding monies due Nortel
                hereunder.

        10.6    The obligations of Nortel hereunder with respect to any suit,
                claim, or proceeding described in Section 10.2 shall not apply
                with respect to Products which are (a) manufactured or supplied
                by Nortel in accordance with any design or any special
                instruction furnished by Buyer, (b) used by Buyer in a manner or
                for a purpose not contemplated by this Agreement, (c) located by
                Buyer outside the United States, or (d) used by Buyer in
                combination with other products not provided by Nortel,
                including, without limitation, any software developed solely by
                Buyer through the permitted use of Products furnished hereunder,
                provided the infringement arises from such combination or the
                use thereof. Buyer shall indemnify and hold Nortel harmless
                against any loss, cost, expense, damage, settlement or other
                liability, including, but not limited to, attorneys' fees, which
                may be incurred by Nortel with respect to any suit, claim, or
                proceeding described in this Section 10.6.

        10.7    Notwithstanding the above, Nortel shall have no obligation or
                liability with regard to any patent infringement suit, claim, or
                proceeding that may be made or brought against Buyer (i)
                alleging that method of use claims in such patent are infringed
                by any service offering and/or by any use by Buyer of Products
                furnished hereunder to make such service offering available or
                (ii) resulting in a settlement payment, or award of damages, or
                accounting of profits, where such settlement, award, or
                accounting is based on the revenues or profits earned or other
                value obtained by Buyer from its use of such Products and/or is
                based on the lost revenues or profits of third parties arising
                from Buyer's use of such Products.

        10.8    If Nortel determines that any Products are or may become the
                subject of a suit, claim, or proceeding as described in Section
                10.7, Nortel may provide Buyer with notice to that effect.
                Nortel shall have no liability to Buyer pursuant to Section
                10.22, 10.4, or 10.5 with respect to Buyer's use of such



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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 6

                Products which occurs subsequent to such notice. In addition to
                its obligations pursuant to Section 10.3, if Buyer becomes aware
                that any Products may become the subject of any such suit,
                claim, or proceeding before receiving any such notice from
                Nortel, Buyer shall provide Nortel with notice to that effect.

        10.9    After receipt of notice from Nortel pursuant to Section 10.8,
                Buyer shall have the option to return to Nortel the applicable
                Products identified in such notice and Nortel shall refund the
                depreciated value (as carried on the books of Buyer) of the
                returned Products to Buyer as more fully set forth in Section
                10-5.

        10.10   The provisions of Sections 10.2 through 10.9 state the entire
                liability of Nortel and its suppliers and the exclusive remedy
                of Buyer with respect to any suits, claims, or proceedings of
                the nature described in Section 10.2.

        10.11   Each party's respective obligations pursuant to this Section
                shall survive any termination of this Agreement.

11.     REMEDIES AND LIMITATION OF LIABILITY

        11.1    Nortel shall have the right to suspend its performance by
                written notice to Buyer and forthwith remove and take possession
                of all Products that shall have been delivered to Buyer, if,
                prior to payment to Nortel of any amounts due pursuant to this
                Agreement with respect to such Products, Buyer shall (a) become
                insolvent or bankrupt or cease, be unable, or admit in writing
                its inability, to pay all debts as they mature, or make a
                general assignment for the benefit of, or enter into any
                arrangement with, creditors, (b) authorize, apply for, or
                consent to the appointment of, a receiver, trustee, or
                liquidator of all or a substantial part of its assets or have
                proceedings seeking such appointment commenced against it which
                are not terminated within ninety (90) days of such commencement,
                or (c) file a voluntary petition under any bankruptcy or
                insolvency law or under the reorganization or arrangement
                provisions of the United States Bankruptcy Code or any similar
                law of any jurisdiction or have proceedings under any such law
                instituted against it which are not terminated within ninety
                (90) days of such commencement.

        11.2    In the event of any material breach of this Agreement which
                shall continue for thirty (30) or more days after written notice
                of such breach (including a reasonably detailed statement of the
                nature of such breach) shall have been given to the breaching
                party by the aggrieved party, the aggrieved party shall be
                entitled at its option to avail itself of any and all remedies
                available at law or equity, except as otherwise provided in this
                Agreement.




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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 7

        11.3    Nothing contained in Section 11.2 or elsewhere in this Agreement
                shall make either party liable for any incidental, indirect,
                consequential or special damages of any nature whatsoever for
                any breach of this Agreement whether the claims for such damages
                arise in tort, contract, or otherwise, or shall increase the
                liability of the breaching party under this Agreement, including
                all Exhibits thereto, beyond that prescribed therein except that
                the foregoing shall not operate to limit Buyer's liability for a
                breach by it of its obligation under the Software License in
                Exhibit B.

        11.4    Any action for breach of this Agreement or to enforce any right
                hereunder shall be commenced within two (2) years after the
                cause of action accrues or it shall be deemed waived and barred.

        11.5    The limitations on either party's liability and other
                obligations set forth in Sections 9, 10, and 11 shall survive
                any termination of this Agreement.

12.     FORCE MAJEURE

        If the performance by a party of any of its obligations under this
        Agreement shall be interfered with by reason of any circumstances beyond
        the reasonable control of that party, including without limitation,
        unavailability of supplies or sources of energy, power failure,
        breakdown of machinery, or labor difficulties, including without
        limitation, strikes, slowdowns, picketing or boycotts, then that party
        shall be excused from such performance for a period equal to the delay
        resulting from the applicable circumstances and such additional period
        as may be reasonably necessary to allow that party to resume its
        performance. With respect to labor difficulties as described above, a
        party shall not be obligated to accede to any demands being made by
        employees or other personnel.

13.     CONFIDENTIAL INFORMATION

        13.1    Each party which receives the other party's Confidential
                Information shall use reasonable care to hold such Confidential
                Information in confidence and not disclose such Confidential
                Information to anyone other than to its employees and employees
                of its affiliates with a need to know. A party that receives the
                other party's Confidential Information shall not reproduce such
                Confidential Information, except to the extent reasonably
                required for the performance of its obligations pursuant to this
                Agreement and in connection with any permitted use of such
                Confidential Information.

        13.2    Buyer shall take reasonable care to use Nortel's Confidential
                Information only for study, operating, or maintenance purposes
                in connection with Buyer's use of Products furnished by Nortel
                pursuant to this Agreement.




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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 8

        13.3    Nortel shall take reasonable care to use Buyer's Confidential
                Information only to perform Nortel's obligations to provide
                Products and/or Services to Buyer, provided Nortel may use any
                of Buyer's Confidential Information for the development,
                manufacture, marketing and maintenance of new products and/or
                services and/or changes or modifications to the existing
                Products and/or Services, which Nortel may, in either case,
                provide to third parties without restriction.

        13.4    The obligations of either party pursuant to this Section 13
                shall not extend to any Confidential Information which recipient
                can demonstrate through written documentation was already known
                to the recipient prior to its disclosure to the recipient, was
                known or generally available to the public at the time of
                disclosure to the recipient, becomes known or generally
                available to the public (other than by act of the recipient)
                subsequent to its disclosure to the recipient, is disclosed or
                made available in writing to the recipient by a third party
                having a bona fide right to do so, or is required to be
                disclosed by process of law, provided that the recipient shall
                notify the disclosing party promptly upon any request or demand
                for such disclosure.

        13.5    The parties' obligations pursuant to this Section 13 shall
                survive any termination of this Agreement for a period of twelve
                (12) months.

14.     BUYER'S RESPONSIBILITIES

        14.1    All sites at which the Products shall be delivered or installed
                shall be prepared by Buyer in accordance with Nortel's
                standards, communicated to Buyer, including, without limitation,
                environmental requirements.

        14.2    Buyer shall provide Nortel-designated personnel reasonable
                access to the Products during the times deemed reasonably
                necessary by Nortel to install, maintain and service the
                Products in accordance with Nortel's obligations. Nortel
                personnel shall comply with Buyer's reasonable site and security
                regulations, provided Nortel receives written notice of any such
                regulations reasonably in advance of the arrival of Nortel's
                personnel at the site.

        14.3    Buyer shall provide reasonable working space and facilities,
                including heat, light, ventilation, telephones, electrical
                current, trash removal and other necessary utilities for use by
                Nortel-designated maintenance personnel, and adequate secure
                storage space, if required by Nortel, for Products and
                materials, provided Nortel gives written notice of the identity
                of its designated maintenance personnel. Buyer shall also
                provide adequate security for the Products while on Buyer's
                site.




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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 9

        14.4    Buyer shall obtain all necessary governmental permits applicable
                to Buyer in connection with the installation, operation, and
                maintenance of Products furnished hereunder, excluding any
                applicable permits required in the normal course of Nortel's
                doing business.

        14.5    Upon written request by Nortel, information which Nortel
                reasonably requests from Buyer and which is necessary for Nortel
                to properly install or maintain the Products shall be provided
                by Buyer to Nortel in a timely fashion and in a form reasonably
                specified by Nortel.

15.     HAZARDOUS MATERIALS

        15.1    Prior to issuing any Order for Services to be performed at
                Buyer's facilities, Buyer shall identify and notify Nortel in
                writing of the existence of all Hazardous Materials which Nortel
                may encounter during the performance of such Services,
                including, without limitation, any Hazardous Materials contained
                within any equipment to be removed by Nortel.

        15.2    If Buyer breaches its obligations pursuant to Section 15.1, (a)
                Nortel may discontinue the performance of the appropriate
                Services until all the applicable Hazardous Materials have been
                removed or abated to Nortel's satisfaction by Buyer at Buyer's
                sole expense, and (b) Buyer shall defend, indemnify and hold
                Nortel harmless from any and all damages, claims, losses,
                liabilities and expenses, including, without limitation,
                attorneys' fees, which arise out of Buyer's breach of such
                obligations. Buyer's obligations pursuant to this Section 15.2
                shall survive any termination of this Agreement.

16.     SUBCONTRACTING

        Nortel may subcontract any of its obligations under this Agreement, but
        no such subcontract shall relieve Nortel of primary responsibility for
        performance of its obligations.

17.     REGULATORY COMPLIANCE

        In the event of any change in the Specifications or Nortel's
        manufacturing or delivery processes for any Products as a result of the
        imposition of requirements by any government, Nortel may upon notice to
        Buyer, increase its prices, charges and fees to cover the added costs
        and expenses directly and indirectly incurred by Nortel as a result of
        such change.




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                                                       AGREEMENT NO. MC-10/96-DM
                                                                         PAGE 10

18.     GENERAL

        18.1    If any of the provisions of this Agreement shall be invalid or
                unenforceable under applicable law and a party deems such
                provisions to be material, that party may terminate this
                Agreement upon notice to the other party. Otherwise, such
                invalidity or unenforceability of any nonmaterial provision
                shall not invalidate or render this Agreement unenforceable, but
                this Agreement shall be construed as if not containing the
                particular invalid or unenforceable provision and the rights and
                obligations of the parties shall be construed and enforced
                accordingly.

        18.2    A party shall not release without the prior written approval of
                the other party any advertising or other publicity relating to
                this Agreement wherein such other party may reasonably be
                identified. In addition each party shall take reasonable
                precautions to keep the existence and the contents of this
                Agreement confidential so long as this Agreement remains in
                effect and for a period of one (1) year thereafter, except as
                may be reasonably required to enforce this Agreement or by law.

        18.3    The construction, interpretation and performance of this
                Agreement shall be governed by the laws of the State of North
                Carolina, except for its rules with respect to the conflict of
                laws.

        18.4    Except as set forth in Section 16 hereof, neither party may
                assign or transfer this Agreement or any of its rights hereunder
                without the prior written consent of the other party, such
                consent not to be unreasonably withheld.

        18.5    Notices and other communications shall be transmitted in writing
                by certified United States Mail, postage prepaid, return receipt
                requested, by guaranteed overnight delivery, or by facsimile
                addressed to the parties as follows:

                To Buyer:    MIDCOM Communications Inc.
                             MIDCOM Tower, Suite 1600
                             1111 Third Avenue
                             Seattle, Washington 98101
                             Attention:       VPA Network
                                              with copy to Law Dept., attention
                                              General Counsel
                             Facsimile:       (206) 628-8295

                To Nortel:   Northern Telecom Inc.
                             350 Lakeside Blvd., Suite 200
                             Richardson, Texas 75083
                             Attention:       Vice President & General Manager
                             Facsimile:       (972) 685-8845



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                                                       AGREEMENT NO. MC-10/96-DM
                                                                         PAGE 11

                In addition, notices submitted by Buyer to Nortel specific to
                any Product Attachment shall be delivered to the address stated
                in the applicable Product Attachment along with a copy submitted
                to Nortel at the address stated above.

                Any notice or communication sent under this Agreement shall be
                deemed given upon receipt, as evidenced by the United States
                Postal Service return receipt Mail if given by certified United
                States Mail, on the following business day if sent by guaranteed
                overnight delivery, or on the transmission date if given by
                facsimile during the receiving party's normal business hours.

                The address information listed for a party in this Section or
                any Product Attachment may be changed from time to time by that
                party by giving notice to the other as provided above.

        18.6    In the event of a conflict between the provisions of this
                Agreement which are not contained in a Product Attachment and
                the provisions of a Product Attachment, the provisions of the
                Product Attachment shall prevail only with respect to the
                Product Line and Services described in that Product Attachment.

        18.7    All headings used herein are for index and reference purposes
                only, and shall not be given any substantive effect. This
                Agreement has been created jointly by the parties, and no rule
                of construction requiring interpretation against the drafter of
                this Agreement shall apply in its interpretation.

        18.8    Buyer shall not export any technical data received from Nortel
                pursuant to this Agreement, or release any such technical data
                with the knowledge or intent that such technical data will be
                exported or transmitted to any country or to foreign nationals
                of any country, except in accordance with applicable U.S. law
                concerning the exporting of such technical data. Buyer shall
                obtain all authorizations from the U.S. government in accordance
                with applicable law prior to exporting or transmitting any such
                technical data as described above.

        18.9    Any changes to this Agreement may only be effected if agreed
                upon in writing by duly authorized representatives of the
                parties hereto. No agency, partnership, joint venture, or other
                similar business relationship shall be or is created by this
                Agreement.




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                                                       AGREEMENT NO. MC-10/96-DM
                                                                         PAGE 12

        18.10   This Agreement, including all Product Attachments and Exhibits
                constitutes the entire agreement of the parties with respect to
                the subject matter hereof.

    NORTHERN TELECOM INC.              MIDCOM COMMUNICATIONS INC.

    By: /s/ VICKIE YOHE                By: /s/ ROBERT J. CHAMBERLAIN
       -------------------------------    ----------------------------------
                (Signature)                        (Signature)

    Name:    Vickie Yohe               Name:  Robert J. Chamberlain
       -------------------------------    ----------------------------------
                (Print)                           (Print)

    Title:  VP & General Manager       Title: Executive Vice President & CFO
       -------------------------------    ----------------------------------

    Date.  3 FEB 97                           Date: 1/27/97
       -------------------------------    ----------------------------------



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                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 1

                                    EXHIBIT A

                                   DEFINITIONS

As used in the Agreement (as defined below), the following initially capitalized
terms shall have the following meanings:

"Affiliate" shall mean Nortel's parent corporation, Northern Telecom Limited and
any corporation controlled directly or indirectly by Northern Telecom Limited or
Midcom Communications Inc., as the case may be, through the ownership or control
of shares or other securities in such corporation.

"Agreement" shall mean the Agreement to which this Exhibit is attached, and all
Exhibits and Product Attachments.

"Confidential Information" shall mean all information, including, without
limitation, specifications, drawings, documentation, know-how and pricing
information, of every kind or description which may be disclosed by either party
or an Affiliate to the other party in connection with this Agreement, provided
the disclosing party shall clearly mark any such information which is disclosed
in writing as the confidential property of the disclosing party and the
disclosing party shall identify the confidential nature of any such information
which it orally discloses at the time of such disclosure and shall provide a
written summary of the orally disclosed information to the recipient within
fifteen (15) days of such disclosure.

"Equipment" shall mean the hardware listed or otherwise identified in, or
pursuant to, any Product Attachment.

"Exhibits" shall mean Exhibits A, B, C, and D attached hereto, and any
additional Exhibits which Nortel and Buyer subsequently agree in writing shall
be incorporated into, and made a part of the Agreement by reference.

"Hazardous Materials" shall mean any pollutants or dangerous, toxic or hazardous
substances (including, without limitation, asbestos) as defined in, or pursuant
to, the OSHA Hazard Communication Standard (29 CFR Part 1910, Subpart Z), the
Resource Conservation and Recovery Act of 1976 (42 USC Section 6901, et seq.),
the Toxic Substances Control Act (15 USC Section 2601, et seq.), the
Comprehensive Environmental Response Compensation and Liability Act (42 USC
Section 9601, et seq.), and any other federal, state or local environmental law,
ordinance, rule or regulation.

"Order" shall mean a written purchase order issued by Buyer to Nortel. Each
Order shall specify on the face of the Order the types and quantities of
Products and/or Services to be furnished by Nortel pursuant to the Order, the
applicable prices, charges and/or fees with respect to such Products and/or
Services,




<PAGE>   14



                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 2

Buyer's facility to which the Products are to be delivered, the delivery and/or
completion schedule, and any other information which may be required to be
included in an Order in accordance with the provisions of this Agreement

"Product Attachments" shall mean any Product Attachments which the parties agree
in writing shall be incorporated into, and made a part of, this Agreement.

"Product Attachment Term" shall mean the period specified in a Product
Attachment during which that Product Attachment shall be in effect.

"Product Line" shall mean the Products described in and which may be furnished
pursuant to a specific Product Attachment.

"Products" shall mean any Equipment and/or Software which may be provided under
this Agreement.

"Services" shall mean all services listed or otherwise identified in, or
pursuant to, any Product Attachment which may be purchased from or provided by
Nortel and which are associated with the Product Line described in that Product
Attachment.

"Software" shall mean (a) programs in machine-readable code or firmware which
(i) are owned by, or licensed to, Nortel or any of its Affiliates, (ii) reside
in Equipment memories, tapes, disks or other media, and (iii) provide basic
logic operating instructions and user-related application instructions, and (b)
documentation associated with any such programs which may be furnished by Nortel
to Buyer from time to time.

"Specifications" shall mean, with respect to any Product Line, the
specifications identified in the applicable Product Attachment, provided Nortel
shall have the right at its sole discretion to modify, change or amend such
specifications at any time.

"Third Party Software Vendor" shall mean any supplier of programs contained in
the Software which is not an Affiliate.

"Vendor Items" shall mean, with respect to a Product Line, those portions of the
Product which are identified in the applicable Product Attachment as Vendor
Items.

"Warranty Period" shall mean, with respect to a Product Line, the Warranty
Period specified in the applicable Product Attachment.


<PAGE>   15
                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 1

                                    EXHIBIT B

                                SOFTWARE LICENSE

1.      Buyer acknowledges that the Software may contain programs which have
        been supplied by, and are proprietary to, Third Party Software Vendors.
        In addition to the terms and conditions herein, Buyer shall abide by
        any additional terms and conditions provided by Nortel to Buyer in
        writing with respect to any Software provided by any Third Party
        Software Vendor.

2.      Upon Buyer's payment to Nortel of the applicable fees with respect to
        any Software furnished to Buyer pursuant to this Agreement, Buyer shall
        be granted a personal, non-exclusive, paid-up license to use the version
        of the Software furnished to Buyer only in conjunction with Buyer's use
        of the Equipment with respect to which such Software was furnished for
        the life of that Equipment as it may be repaired or modified. Buyer
        shall be granted no title or ownership rights to the Software, which
        rights shall remain in Nortel or its suppliers.

3.      As a condition precedent to this license and to the supply of Software
        by Nortel pursuant to the Agreement, Nortel requires Buyer to give
        proper assurances to Nortel for the protection of the Software.
        Accordingly, all Software supplied by Nortel under or in implementation
        of the Agreement shall be treated by Buyer as the exclusive property,
        and as proprietary and a TRADE SECRET, of Nortel and/or its suppliers,
        as appropriate, and Buyer shall: a) hold the Software, including,
        without limitation, any methods or concepts utilized therein in
        confidence for the benefit of Nortel and/or its suppliers, as
        appropriate; b) not provide or make the Software available to any person
        except to its employees on a 'need to know' basis; c) not reproduce,
        copy, or modify the Software in whole or in part except as authorized by
        Nortel; d) not attempt to decompile, reverse engineer, disassemble,
        reverse translate, or in any other manner decode the Software; e) issue
        adequate instructions to all persons, and take all actions reasonably
        necessary to satisfy Buyer's obligations under this license; and f)
        forthwith return to Nortel, or with Nortel's consent destroy, any
        magnetic tape, disc, semiconductor device or other memory device or
        system and/or documentation or other material, including, but not
        limited to all printed material furnished by Nortel to Buyer which shall
        be replaced, modified or updated.

4.      The obligations of Buyer hereunder shall not extend to any information
        or data relating to the Software which is now available to the general
        public or becomes available by reason of acts or failures to act not
        attributable to Buyer.




<PAGE>   16



                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 2

5.      Buyer shall not assign this license or sublicense any rights herein
        granted to any other party except an Affiliate of Buyer without Nortel's
        prior written consent, provided such Affiliate agrees in writing to be
        bound by the terms of this Software License.

6.      Each party shall indemnify and hold the other and its suppliers, as
        appropriate, harmless from any loss or damage resulting from a breach of
        this Exhibit B. The obligations of the parties under this Exhibit B
        shall survive the termination of the Agreement and shall continue if the
        Software is removed from service.



<PAGE>   17



                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 1

                                    EXHIBIT C

                                     STORAGE

If Buyer notifies Nortel prior to the scheduled shipment date of Products that
Buyer does not wish to receive such Products on the date agreed by the parties,
or the installation site or other delivery location is not prepared in
sufficient time for Nortel to make delivery in accordance with such date, or
Buyer fails to take delivery of any portion of such Products, Nortel may place
the applicable Products in storage. In that event Buyer shall be liable for all
additional costs thereby incurred by Nortel. Delivery by Nortel of any Products
to a storage location as provided above shall be deemed to constitute delivery
of the Products to Buyer for purposes of this Agreement, including, without
limitation, provisions for payment, invoicing, passage of risk of loss,
and commencement of the Warranty Period.




<PAGE>   18



                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 1

                                    EXHIBIT D

                         LIMITED WARRANTIES AND REMEDIES

1.      Nortel warrants that the Equipment supplied hereunder will under normal
        use and service be free from defective material and faulty workmanship
        and will conform to the applicable Specifications for the Warranty
        Period specified in the Product Attachment with respect to such
        Equipment. The foregoing warranty shall not apply to items normally
        consumed in operation, such as, but not limited to, lamps and fuses or
        to Vendor Items. Nortel covenants and warrants that any installation
        Services performed by Nortel with respect to such Equipment shall be
        free from defects in workmanship for the Warranty Period set forth in
        the applicable Product Attachment.

2.      Nortel's sole obligation and Buyer's exclusive remedy under the warranty
        and covenants set forth in Section 1 above shall be limited to the
        replacement or repair, at Nortel's option and expense, of the defective
        Equipment, or correction of the defective installation Services.
        Replacement Equipment may be new or reconditioned at Nortel's option.

3.      Nortel covenants and warrants that any Software licensed by Nortel to
        Buyer under this Agreement shall function during the Warranty Period of
        the Equipment with respect to which such Software is furnished without
        any material, service-affecting nonconformance to the applicable
        Specifications, provided that Buyer shall have paid all Software support
        fees specified in the applicable Product Attachment. If the Software
        fails to so function, Buyer's sole remedy and Nortel's sole obligation
        under this covenant and warranty is for Nortel to correct such failure
        through, at Nortel's option, the replacement or modification of the
        Software or such other actions as Nortel reasonably determines to be
        appropriate.

4.      Unless otherwise stated in a Product Attachment, (a) Nortel's covenant
        and warranty in Section 3 above shall only apply to the portion of the
        Software actually developed by Nortel or its Affiliates, (b) all other
        Software shall be provided by Nortel "AS IS", (c) Nortel shall assign to
        Buyer on a nonexclusive basis any warranty on such other Software
        provided to Nortel by the developer of such other Software to the extent
        of Nortel's legal right to do so.

5.      The obligations and remedies set forth in Sections 1, 2, and 3 above
        shall be conditional upon: the Equipment not having been altered or
        repaired, the Software not having been modified, and the Products not
        having been installed outside the United States; any defect or
        nonconformance not being the result of mishandling, abuse, misuse,
        improper storage, improper performance of installation, other services,
        maintenance or operation by other than Nortel (including use in
        conjunction with any product which is incompatible with the applicable
        Equipment or Software or of inferior performance), and/or any error,




<PAGE>   19



                                                       AGREEMENT NO. MC-10/96-DM
                                                                          PAGE 2

        act, or omission of Buyer described in Section 11.4; the Product not
        having been damaged by fire, explosion, power failure, power surge, or
        other power irregularity, lightning, failure to comply with all
        applicable environmental requirements for the Products specified by
        Nortel or any other applicable supplier, such as but not limited to
        temperature or humidity ranges, or any act of God, nature or public
        enemy; and written notice of the defect having been given to Nortel
        within the applicable Warranty Period.

6.      The performance by Nortel of any of its obligations described in Section
        2 or 3 of this Exhibit D shall not extend the applicable Warranty Period
        except to the extent specified in the applicable Product Attachment.

7.      Upon expiration of the applicable Warranty Period for Equipment
        furnished hereunder, repair and replacement Service for such Equipment
        shall be available to Buyer from Nortel in accordance with Nortel's
        then-current terms, conditions and prices. Such repair and replacement
        Service and notice of any discontinuance of such repair and replacement
        Service shall be available for a minimum period set forth in the Product
        Attachment applicable to such Equipment. This provision shall survive
        the expiration of this Agreement.

8.      Unless Nortel elects to repair or replace defective Equipment at Buyer's
        facility, all Equipment to be repaired or replaced, whether in or out of
        warranty, shall be packed by Buyer in accordance with Nortel's
        instructions stated in the applicable Product Attachment and shipped at
        Buyer's expense and risk of loss to a location designated by Nortel.
        Replacement Equipment shall be returned to Buyer at Nortel's expense and
        risk of loss. Buyer shall ship the defective Equipment to Nortel within
        thirty (30) days of receipt of the replacement Equipment. In the event
        Nortel fails to receive such defective Equipment within such thirty (30)
        day period, Nortel shall invoice Buyer for the replacement Equipment at
        the then current Nortel price for such.

9.      With respect to any Vendor Item furnished by Nortel to Buyer pursuant to
        this Agreement, Nortel shall assign to Buyer on a nonexclusive basis any
        warranty granted by the party that supplied such Vendor Item to Nortel
        to the extent of Nortel's right to do so.

10.     Neither Nortel nor Nortel's suppliers, as appropriate, shall have any
        responsibility for warranties offered by Buyer to any of its customers.
        Buyer shall indemnify Nortel and Nortel's suppliers, from and against
        all claims, losses and actual damages, reasonable costs and expenses
        (including ordinary and necessary attorneys fees) ("Losses") arising
        directly out of a warranty offered by Buyer to its customers. Nortel or
        Nortel's suppliers shall first give written notice of any claim and
        tender the defense of the applicable suit, claim or proceeding to Buyer.




<PAGE>   20



                                                              Product Attachment
                                                                          Page 1

                                                                         st7286h

                               PRODUCT ATTACHMENT
                            CARRIER NETWORKS PRODUCTS

Northern Telecom Inc. ("Nortel") and MIDCOM Communications Inc., ("Buyer") agree
as follows:

1.      INCORPORATION BY REFERENCE

        This Product Attachment ("Attachment") shall be incorporated into and
        made a part of the Network Products Purchase Agreement No. MC-10/96-DM
        (the "Agreement") between Nortel and Buyer.

2.      DEFINITIONS

        For purposes of this Attachment:

        "Acceptance Criteria" shall mean, with respect to any Products installed
        by Nortel hereunder, the standards and specifications contained in the
        Nortel Installation Manuals which are applicable to such Products.

        "Equipment" shall mean the equipment listed in Schedule A.

        "Extension" shall mean Equipment and/or Software which Nortel engineers
        and installs and which is added to an Initial System after the Turnover
        Date of the Initial System.

        "Initial System" shall mean the Equipment and Software which is included
        in any configuration identified in Schedule A as an "Initial System."

        "Installation Site" shall mean Buyer's facility identified in an Order
        to which the applicable Products identified in such Order shall be
        delivered or at which the applicable Services, if any, are to be
        performed, respectively.

        "Merchandise" shall mean any Equipment which is not part of a System and
        with respect to which no engineering or installation Services shall be
        provided by Nortel.

        "Attachment Term" shall mean the period which shall commence on the date
        this Attachment is executed by the latter of the parties and shall
        expire sixty (60) months thereafter.

        "Services" shall mean the services described in Schedule B.




<PAGE>   21



                                                              Product Attachment
                                                                          Page 2

         "Software" shall mean the software listed in Schedule A.

         "Specifications" shall mean with respect to any Products furnished
         hereunder, the specifications published by Nortel which Nortel
         identifies as its standard performance specifications for such Products
         as of the date of Buyer's Order for such Products.

         "System" shall mean any Initial System or Extension.

         "Turnover Date" shall mean, with respect to any Products installed by
         Nortel hereunder, the date on which Nortel provides the Turnover Notice
         to Buyer pursuant to Section 7.a. of this Attachment.

         "Warranty Period" shall mean, with respect to:

         (a)      Any System, the period which shall commence upon the Turnover
                  Date with respect to such System and shall expire twelve (12)
                  months thereafter,

         (b)      Merchandise, the period which shall commence upon the date of
                  shipment with respect to such Merchandise by Nortel to Buyer
                  and shall expire ninety (90) days thereafter,

         (c)      Installation Services involving any System, the period which
                  shall commence upon the Turnover Date with respect to such
                  System and shall expire twelve (12) months thereafter,

         (d)      Equipment which is repaired or replaced pursuant to Nortel's
                  obligations under Exhibit D to the Agreement, the period
                  commencing five (5) days after (i) shipment of the replacement
                  Equipment to Buyer or (ii) completion of the repair at the
                  Installation Site of the applicable Equipment and which shall
                  expire on the later of thirty (30) days. thereafter or the
                  last day of the original Warranty Period with respect to the
                  Equipment which was repaired or replaced, and

         (e)      Software which was corrected pursuant to Nortel's obligations
                  under Exhibit D to the Agreement, the period commencing upon
                  delivery of the corrected Software by Nortel to Buyer and
                  expiring on the later of thirty (30) days thereafter or the
                  last day of the original Warranty Period with respect to such
                  Software.

3.       SCHEDULES

         The following Schedules which are attached hereto are an integral part
         of the Attachment and are incorporated herein by reference:




<PAGE>   22



                                                              Product Attachment
                                                                          Page 3


                  Schedule A        - Products, Prices, and Fees
                  Schedule B        - Services and Charges
                  Schedule C        - Delivery
                  Schedule D        - Documentation

4.      ORDERING

        With respect to Section 3, ORDERING of the Agreement the following
        additional terms shal1 apply:

a.      Buyer shall identify in each Order for Products whether the Products
        constitute an Initial System, Extension, or Merchandise. All Orders for
        Extensions, Merchandise, or any Services other than engineering and
        installation Services provided by Nortel in connection with an Order for
        an Initial System shall be subject to written agreement of Buyer and
        Nortel on the applicable prices, charges and fees with respect thereto
        as required pursuant to Section 5, PRICING, of this Attachment.

b.      Notwithstanding Exhibit C to the Agreement, Buyer may by written notice
        to Nortel cancel without charge any Order for Products and/or Services
        prior to the delivery date of the applicable Products set forth in such
        Order or the agreed date for the commencement by Nortel of the
        applicable Services ("Service Commencement Date"), except that if Buyer
        cancels such Order within five (5) weeks or less of any such date, a
        cancellation fee of eight percent (8%) of the aggregate price of all
        Products and/or Services included in such cancelled Order shall be
        payable by Buyer. Nortel may invoice such amount upon receipt of Buyer's
        notice of cancellation of the Order.

C.      Notwithstanding Exhibit C to the Agreement, Buyer may by written notice
        to Nortel not less than six (6) weeks prior to the delivery date of any
        Products set forth in an Order and/or the Service Commencement Date of
        the applicable Services, delay the delivery date of such Products and/or
        the Service Commencement Date of such Services for a period which shall
        not exceed ninety (90) days from the date such Products were originally
        scheduled to be delivered or ninety (90) days from the Service
        Commencement Date, subject to the availability from Nortel of the
        applicable Products and/or Services after such period of delay.

d.      Except as set forth in Sections 4.b. and 4.c. of this Attachment, any
        change to an Order after Nortel's acceptance of such Order shall require
        written agreement of Nortel and Buyer upon a written change to the Order
        ("Change Order") which shall reference the original Order and be
        executed by the parties. No such changes shall be implemented until the
        applicable Change Order has been executed by the parties.




<PAGE>   23



                                                              Product Attachment
                                                                          Page 4

e.      With respect to each Order for Products which is accepted by Nortel,
        Buyer may make a written request at least ninety (90) days prior to the
        scheduled shipment date of such Products for a change ("Change")
        consisting of certain addition(s) or deletion(s) to such Products. After
        receipt of such request, Nortel shall submit a Job Change Order ("JCO")
        to Buyer for Buyer's approval with respect to the requested Change,
        except that Nortel shall be under no obligation to submit such JCO to
        Buyer if Nortel determines that the Price applicable to such Order would
        be reduced by more than ten percent (10%) as a result of the
        implementation of the Change. Each JCO shall state whether the
        requested Change shall increase or decrease the Price and/or time
        required by Nortel for any aspect of its performance under the Agreement
        with respect to such Order. Buyer shall accept or reject the JCO in
        writing within ten (10) days of receipt thereof. Failure of the Buyer to
        accept or reject the JCO in writing as described above shall be deemed a
        rejection of the JCO by Buyer. In the event an accepted JCO involves the
        return to Nortel of any Equipment which shall have been previously
        delivered to Buyer, Nortel may invoice and Buyer shall pay the
        transportation costs and Nortel's then-current restocking charge for the
        returned Equipment.

f.      Any increase or decrease in the Price with respect to an Order hereunder
        which is occasioned by an accepted JCO shall be added to or subtracted
        from, as applicable, the amount of the last payment due pursuant to
        Section 6 with respect to such Order.

g.      If Buyer rejects a proposed JCO, then the rights and obligations of the
        parties with respect to the applicable Order shall not be subject to
        Buyer's requested Changes, provided that Buyer shall promptly pay to
        Nortel all of Nortel's additional costs and expenses incurred hereunder
        in accordance with Buyer's requested Changes and Nortel's additional
        costs and expenses subsequently incurred in order that Nortel may be
        able to perform Nortel's obligations without modification by the
        requested Changes, and Nortel shall be entitled to an extension of the
        dates for performance of its obligations with respect to the applicable
        Order as a result of any delays in such performance which result from
        the foregoing.

5.      PRICING

        With respect to Section 4, PRICES of the Agreement, the following
        additional terms shall apply:

a.      The prices set forth in Schedule A with respect to any Initial System
        shall be in effect for a period which shall commence upon the effective
        date of this Attachment and shall expire after six (6) months. Nortel
        may in its sole discretion, thereafter, increase any prices set forth in
        Schedule A upon sixty (60) days prior written notice to Buyer. The
        prices listed in Schedule A shall apply to




<PAGE>   24



                                                              Product Attachment
                                                                          Page 5

        any Order for an Initial System listed in Schedule A which shall be
        received by Nortel prior to the effective date of any change in such
        prices as permitted by this Section, provided that delivery date for
        such Initial System as set forth in the applicable Order shall be not
        more than one-hundred twenty (120) days after Nortel's acceptance of
        such Orders.

b.      The prices for Equipment and the fees for the right to use the Software
        included in any Extension, prices for any Merchandise, and charges for
        any Services, other than engineering and installation Services provided
        with any Initial System shall be as subsequently agreed in writing by
        Nortel and Buyer.

c.      All transportation charges associated with the shipment of the Products
        to Buyer shall be payable by Buyer. Buyer shall promptly reimburse
        Nortel for any such charges which may be incurred by Nortel.

6.      TERMS OF PAYMENT

        With respect to Section 5, TERMS OF PAYMENT, the following additional
        terms shall apply:

a.      With respect to each Initial System furnished hereunder by Nortel to
        Buyer the price listed in Schedule A shall be invoiced by Nortel in
        accordance with the following schedule:

        (i)     Twenty percent (20%) of such price may be invoiced upon Nortel's
                acceptance of the Order for such Initial System,

        (ii)    Fifty percent (50%) of such price may be invoiced on the date of
                shipment by Nortel to Buyer of the switch component of such
                Initial System,

        (iii)   Twenty percent (20%) of such price may be invoiced on the
                Turnover Date of such Initial System, and

        (iv)    Ten percent (10%) of such price may be invoiced on the date of
                Acceptance of such Initial System.

b.      With respect to each Extension furnished hereunder by Nortel to Buyer,
        the applicable price determined in accordance with Section 5.b. of this
        Attachment shall be invoiced by Nortel in accordance with the following
        schedule:

        (i)     Twenty percent (20%) of such price may be invoiced upon Nortel's
                acceptance of the Order for such Extension,

        (ii)    Fifty percent (50%) of such price may be invoiced on the date
                of shipment by Nortel to Buyer of the Equipment included in such
                Extension,




<PAGE>   25



                                                              Product Attachment
                                                                          Page 6

        (iii)   Twenty percent (20%) of such price may be invoiced on the
                Turnover Date with respect to such Extension, and

        (iv)    Ten percent (10%) of such price may be invoiced on the date of
                Acceptance of such Extension.

c.      Except as may be otherwise agreed in writing by the parties Nortel's
        prices for Merchandise and charges for any Services determined in
        accordance with Section 5.b. above may be respectively invoiced upon
        delivery of such Merchandise and upon performance of such Services by
        Nortel.

7.      TESTING, TURNOVER, AND ACCEPTANCE

        Pursuant to Section 8.1 of the Agreement, the rights and obligations of
        the parties with respect to testing, turnover and acceptance of any
        Products furnished hereunder and installed by Nortel shall be as
        follows:

a.      Nortel shall provide Buyer with five (5) days written notice prior to
        commencing final commissioning and testing of any Products installed by
        Nortel. Buyer shall cause an authorized representative of Buyer to be
        present at the applicable Installation Site to witness such final
        commissioning and testing, provided that in the event such
        representative fails to be present for any reason, Nortel shall not be
        required to delay performance of such final commissioning and testing.
        In connection with the final commissioning and testing of such Products,
        Nortel shall test the Products for conformity with the applicable
        Acceptance Criteria. When such tests have been successfully completed,
        Nortel shall provide Buyer with written notice ("Turnover Notice") that
        the applicable Products meet such Acceptance Criteria and are ready for
        Buyer's testing for compliance with such Acceptance Criteria. Buyer
        shall promptly complete and return to Nortel Buyer's acknowledgment of
        receipt of such Turnover Notice.

b.      Following the Turnover Date, Buyer may test the applicable Products for
        compliance with the Acceptance Criteria using the tests and test
        procedures contained in Nortel's Installation Manuals with respect to
        such Products. Within fifteen (15) business days following the Turnover
        Date of the applicable Products, Buyer shall notify Nortel either that
        Buyer has accepted such Products in writing using Nortel's standard
        Acceptance Notice form or that Buyer has not accepted such Products in
        which case Buyer shall also provide Nortel with a written notice
        ("Notice of Deficiency") which shall provide in reasonable detail the
        manner in which Buyer asserts that the Products failed to meet the
        Acceptance Criteria. With respect to any such details with which Nortel
        agrees, Nortel shall promptly proceed to take appropriate corrective
        action and following correction, Buyer may retest the Products in
        accordance with this Section. Buyer shall accept the Products in writing
        without delay when the tests




<PAGE>   26



                                                              Product Attachment
                                                                          Page 7

        pursuant to this Section indicate that the Products comply with the
        Acceptance Criteria.

c.      With respect to any points of disagreement between Nortel and Buyer
        concerning any Notice of Deficiency which are not resolved by Nortel and
        Buyer within fifteen (15) business days after the effective date of the
        Notice of Deficiency, Buyer, at its option, may waive any rights it may
        have on account of any such points of disagreement, or require that the
        disputed points be resolved by arbitration.

d.      Buyer shall notify Nortel in writing of its election pursuant to Section
        7.c. not later than fifteen (15) days after the effective date of the
        Notice of Deficiency, if any, given to Nortel by Buyer. Upon expiration
        of such fifteen (15) day period unless Buyer has notified Nortel to the
        contrary, Buyer shall be deemed to have elected to waive its right with
        respect to any points of disagreement then existing between it and
        Nortel with respect to such Notice of Deficiency.

e.      If Buyer makes timely election to require arbitration of such disputed
        points, the arbitrator shall be chosen by mutual agreement. If the
        parties cannot agree upon an arbitrator within three (3) days of Buyer's
        election to arbitrate, each party shall within three (3) days thereafter
        select an independent and an unaffiliated person to be an arbitrator.
        These two (2) persons selected shall select a third person, independent
        and unaffiliated with either party, as a third arbitrator. The
        arbitration shall be conducted in accordance with the Rules of the
        American Arbitration Association, provided, however that the
        Arbitrator(s) shall be empowered to reduce the Prices of Products only
        to the extent that the Arbitrator(s) find that the benefit of Buyer's
        bargain has been reduced. The Arbitrator(s) shall not have any authority
        to grant partial or total rescission unless the Arbitrator(s) determine
        that (i) Buyer has not substantially received the benefit of its
        bargain; and (ii) money damages will not provide an adequate remedy.
        Judgment upon the award rendered by the Arbitrator(s) may be entered in
        any Court of competent jurisdiction.

f.      For purposes of this Attachment, "Acceptance" of the applicable
        Products shall occur upon the earliest of the following and Buyer shall
        upon request sign Nortel's Acceptance Notice confirming such Acceptance
        without any conditions, restrictions, or limitations of any nature
        whatsoever:

        (i)     The date on which Buyer accepts such Products pursuant to
                Section 7.b. of this Attachment;

        (ii)    The failure of Buyer to provide Nortel with any notice required
                by Section 7.b. of this Attachment, with respect to such
                Products;



<PAGE>   27



                                                              Product Attachment
                                                                          Page 8

        (iii)   Use by Buyer of such Products or any portion thereof in revenue-
                producing service at any time; or

        (iv)    Waiver by Buyer of its rights pursuant to Section 7.c. or 7.d.

g.      Acceptance by Buyer of such Products pursuant to Section 7.f. of this
        Attachment above shall not be withheld or postponed due to:

        (i)     Deficiencies of such Products resulting from causes (A)
                attributable to Buyer, such as, but not limited to (1)
                inaccuracy of information provided by Buyer or, (2) inadequacy
                or deficiencies of any materials, facilities or services
                provided directly or indirectly by Buyer and tested in
                conjunction with the applicable Products, and (B) other
                conditions external to the Products which are beyond the limits
                specified by Nortel in the Specifications for the Products and
                which are used by Nortel in performance calculations with
                respect to the Acceptance Criteria, or spurious outputs from
                adjacent material; or

        (ii)    Minor deficiencies or shortages with respect to such Products
                which are attributable to Nortel, but of a nature that do not
                prevent full and efficient operation of the Products.

h.      With respect to any deficiencies of the type described in Section
        7.g.(i), Nortel shall at Buyer's request and expense assist Buyer in the
        elimination or minimization of any such deficiencies. With respect to
        any deficiencies or shortages as described in the Section 7.g.(ii),
        Nortel shall, at Nortel's expense, take prompt and effective action to
        correct any such deficiencies or shortages.

i.      In the event Buyer's Acceptance of any Products is withheld or postponed
        due to any deficiencies of the type described in Section 7.g.(i), Nortel
        shall invoice and Buyer shall pay Nortel's ordinary and necessary
        charges and expenses incurred by Nortel associated with Nortel's
        investigation of the reasons for Buyer's withholding or postponement of
        such Acceptance.

8.      WARRANTIES AND REMEDIES

        With respect to Exhibit D of the Agreement, LIMITED WARRANTIES AND
        REMEDIES, the following additional terms shall apply:

a.      Except as set forth in Section 8.b. below, Nortel shall in performance
        of its obligations under Section 2 of Exhibit D to the Agreement, (i)
        ship replacement Equipment or complete the repair within thirty (30)
        days of Nortel's receipt of the Equipment to be replaced or repaired,
        and (ii) commence the correction of the applicable installation Services
        within thirty (30) days of receipt of notice from Buyer pursuant to
        Section 5 of Exhibit D to the Agreement.




<PAGE>   28



                                                              Product Attachment
                                                                          Page 9

b.      For emergency warranty service situations involving the Equipment,
        Nortel shall during the applicable Warranty Period use all reasonable
        efforts to ship replacement Equipment within twenty-four (24) hours of
        notification of the applicable warranty defect by Buyer pursuant to
        Section 5 of Exhibit D to the Agreement, provided that Buyer shall have
        requested such emergency service. Nortel may invoice Buyer and Buyer
        shall pay Nortel's surcharge for emergency warranty services. If Nortel
        determines that due to the particular circumstances, onsite technical
        assistance is necessary, Nortel shall use all reasonable efforts to
        dispatch emergency service personnel to the applicable Installation Site
        within twenty-four (24) hours of receipt of notice from Buyer as
        described above.

c.      All Products to be repaired or replaced, both within and outside of the
        applicable Warranty Period, shall be packed by Buyer in accordance with
        Nortel's then current instructions.

d.      No later than ninety (90) days prior to the expiration of the Warranty
        Period with respect to any Initial System, Nortel shall offer to Buyer
        post-warranty support by means of an extended service plan or other
        terms, provided that neither party shall have any obligation with
        respect thereto except as may be agreed upon in writing by the parties.

9.      NOTICES

        Pursuant to Section 18.5 of the Agreement, any notices by Buyer to
        Nortel which are specific to this Attachment shall be delivered to the
        following address:

                        Northern Telecom Inc.
                        2350 Lakeside Blvd.
                        Richardson, Texas 75082-4399
                        Attn: Vice President & General Manager, Carrier Networks

10.     ADDITIONAL TERMS

        The following additional terms shall apply to the Agreement:

(a)     With respect to Section 14, BUYER'S RESPONSIBILITIES, the following
        additional terms shall apply:

        (i)     Buyer shall be responsible for ordering and coordinating with
                each applicable local telephone company the installation of all
                central office trunks and test trunks and Buyer shall be
                responsible for all utility charges associated with the
                installation, testing, operation and maintenance of Products
                furnished hereunder, including, but not limited to, all
                applicable charges for such central office trunks, test trunks
                and any tie lines.



<PAGE>   29



                                                              Product Attachment
                                                                         Page 10

(b)     Nortel shall provide documentation with respect to the Products in
        accordance with Schedule D to this Attachment

(c)     Upon execution of this Product Attachment, Buyer shall issue Orders to
        Nortel for Product(s) and/or Services, as identified herein, for
        delivery during the Product Attachment Term, with an aggregate dollar
        value of no less than that associated with Commitment Level 4, as
        defined in Schedule A, Section VI, subparagraph 1.0 ("Commitment Level
        4"). In the event Buyer fails to satisfy this commitment by the
        expiration or earlier termination of this Product Attachment Term,
        Nortel shall invoice Buyer, and Buyer shall pay, the difference between
        the prices, charges and/or fees Buyer paid for the Product and/or
        Services and the prices, charges and/or fees that Buyer would have paid
        for the Products and/or Services actually ordered by Buyer, based upon
        the prices, fees and/or charges associated with the Commitment Level,
        -for the aggregate dollar value of Products and/or Services which were
        actually ordered by Buyer ("Actual Orders"). Buyer shall pay such
        invoice, including all applicable taxes associated therewith, within
        thirty (30) days from the date of such invoice.

(d)     In consideration for the commitment made by Buyer under subparagraph (c)
        above, the prices, charges and/or fees for the Products and/or Services
        shall be based upon the prices, charges and/or fees, and/or applicable
        discounts set forth in Schedule A.

(e)     In order to begin to satisfy its commitment under subsection (c) above,
        Buyer shall issue an Order or Orders for either (1) six (6) Initial
        Systems, as defined in Schedule A, Section I, subparagraphs 1.0 through
        6.0, at the prices set forth in Schedule A, Section VI, subparagraph
        2.0; or (2) five (5) DMS-250 to DMS-500 Upgrades as defined in Schedule
        A, Section V, subparagraph 1.0, at the prices set forth in Schedule A,
        Section VI, subparagraph 8.0. To the extent Buyer's Order or Orders for
        the foregoing are not sufficient to satisfy Buyer's commitment under
        subsection (c) above, Buyer shall issue an Order of Order(s) to Nortel
        for the Product(s) identified below:

                  Product                            Schedule A Section

                  Link Peripheral Processor                   II
                  Add-On Port Extension                       III
                  Extension Ports                             IV
                  DMS-500 Optional Features                   VIII
                  DMS-250 Optional Features                   X

        Notwithstanding the foregoing, in the event Buyer issues an Order or
        Orders for Product(s) and/or Services in excess of the aggregate dollar
        value associated with Commitment Level 4 during the Attachment Term, or
        in the event Buyer invoices its commitment, the prices, charges, fees
        and/or discounts associated with Commitment Level 4 shall not be
        adjusted retroactively. An Order or Orders for Products and/or Services
        in excess of the dollar value associated with Commitment Level 4 shall
        be subject to the prices, charges, fees and/or applicable discounts
        associated with the appropriate Commitment Level.

        With respect to Schedule A, Section 11, subparagraph 1.0, Link
        Peripheral Processor(s), the prices for such Link Peripheral Processors
        do not include engineering or installation.




<PAGE>   30



                                                              Product Attachment
                                                                         Page 11

(f)     In respect to Schedule A, Section II, subparagraph 1.0, Link Peripheral
        Processor(s) if Ordered, such Link Peripheral Processors are furnished
        less any Nortel engineering or installation.

(g)     Buyer shall not issue any Order for Product hereunder until such time as
        Buyer has secured financing sufficient to cover any such Order. Buyer
        shall have no commitment pursuant to paragraph 10 (c), (d) or (e) above
        until such time as Buyer has issued its first Order for Product
        hereunder.

    NORTHERN TELECOM INC.              MIDCOM COMMUNICATIONS INC.

    By: /s/ VICKIE YOHE                By: /s/ ROBERT J. CHAMBERLAIN
       -------------------------------    ----------------------------------
                (Signature)                        (Signature)

    Name:    Vickie Yohe               Name:  Robert J. Chamberlain
       -------------------------------    ----------------------------------
                (Print)                           (Print)

    Title:  VP & General Manager       Title: Executive Vice President & CFO
       -------------------------------    ----------------------------------

    Date:  3 FEB 97                    Date: 1/27/97
       -------------------------------    ----------------------------------

<PAGE>   31



                                                              Product Attachment
                                                                         Page 12

                                   SCHEDULE A

                            PRODUCTS PRICES AND FEES




<PAGE>   32
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                               I. INITIAL SYSTEMS

NORTEL SHALL ENGINEER EACH OF THE INITIAL SYSTEM(S) ORDERED HEREUNDER IN
ACCORDANCE WITH NORTEL'S STANDARD ENGINEERING PRACTICES AND PROCEDURES, AND
THEREAFTER NORTEL SHALL PROVIDE BUYER WITH A DETAILED LIST OF THE COMPONENTS OF
SUCH INITIAL SYSTEM(S).

1.0     INITIAL SYSTEM DMS-500 13440 PORT MODEL (MODEL A-NEW YORK)

        1.1  The following represents the SuperNode equipment that will be
             delivered with the Initial System DMS-500 13440 Port Model equipped
             with 11040 and wired for 11520 DTEI trunking ports, and equipped
             and wired for 1920 LTEI trunking ports:

             a)  SuperNode front end, Link Peripheral Processor, Enhanced
                 Network and other common equipment as follows:

                 -  SuperNode equipped with BRISC60 processor, five (5) 96 meg
                    memory cps per plane and SLM III.

                 -  Link Peripheral Processor equipped with eight (8) Link
                    Interface Units, (2) Ethernet Interface Units and wired for
                    thirty six (36) Link Interface Units (LIUs). Four of the
                    eight equipped LIUs will be utilized for interworking.

                 -  V.35 Link Peripheral Processor Interface equipment to
                    support an equipped configuration of eight (8) Interface
                    Units and a wired configuration of thirty six (36) Interface
                    Units.

                 -  Twelve (12) Digital Trunk equipment ISDN Ready (DTEI)
                    frames equipped with 11040 and wired for 11520 total
                    trucking ports. Ten thousand five hundred sixty (10560)
                    ports are equipped for SS7 and eleven thousand forty ports
                    (11,040) are wired for SS7. Four hundred eighty (480) ports
                    are equipped and wired for PRI functionality. Nine hundred
                    and sixty (960) ports of the ten thousand five hundred and
                    sixty (10560) equipped SS7 ports will be used for
                    interworking. All DTCIs are equipped with the latest XPM and
                    Universal Tone Receivers for digit collection. Ten thousand
                    five hundred sixty (10560) trunks are equipped with Special
                    Tone Receivers for Reorigination, and Continuity Tone
                    Detectors for SS7 functionality.

                 -  Two (2) Line Trunk equipment ISDN Ready (LTEI) frames
                    wired and equipped with 1920 SS7 ports.

                 -  Two (2) Integrated Services Module (ISM) frames equipped
                    with DMS-500 service and test circuits providing DMS-500
                    functionality, as well as, six (6) Enhanced Digital Recorded
                    Announcement Machine circuit-packs.

                 -  Two (2) Input Output equipment (IOE) frames equipped with:

                    -   One (1) Mag Tape Device

                    -   Four (4) SCSI Disk Drive Units

                    -   Three (3) IOC Shelves

                    -   Three (3) I/O Controllers providing eight (12) switch
                        interface ports

                    -   Four (4) X-25 Automatic File Transfer circuit packs 

                 -  Two (2) MIS frames equipped with the required 500W inverters
                    and terminal block assemblies.

                 -  Two (2) Meridian Cabinet Spare Storage (MCSS) cabinets
                    to house switch spares.

                 -  Two (2) Power Distribution Center (PDC) frames equipped
                    with "A" and "B" feed fuse panels & fuses as required.

December 3, 1996





<PAGE>   33



                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

        1.1     INITIAL SYSTEM DMS-500 13440 PORT MODEL-A NEW YORK CONT.

                        -       Miscellaneous equipment as follows:

                                -       Two (2) Maintenance Administration
                                        Positions & one set of Furniture

                                -       Five (5) UDS 2440 Modems

                                -       One (1) Norstar Key System

                                -       Two (2) M7310 Feature sets to support
                                        Norstar Key System

                                -       Two (2) RTIF Terminals

                                -       One (1) MAP Printer

                                -       One (1) Helmsman Workstation, CD ROM
                                        Software and Printer

                        -       DSX panels to support an eleven thousand forty
                                (11040) equipped port DMS-500 Initial System.

                b)      Single frame enhanced network to support an eleven
                        thousand forty (11040) equipped port DMS-500 Initial
                        System.

                c)      Initial System DMS-500 Port Model Standard Features
                        (Base and Optional) as set forth in Section VII of this
                        Schedule A.

                d)      Nortel's standard complement of DMS-500 Initial System
                        spares.

        1.2     INITIAL SYSTEM DMS-500 13440 PORT MODEL A NEW YORK PRICING

                Refer to Section VI of this Schedule A for detailed Initial
                System Model Pricing.

        1.3     INITIAL SYSTEM DMS-500 13440 PORT MODEL A NEW YORK OPTIONAL
                POWER PLANT PRICING

                The price for Optional Power Plant to support the Initial System
                DMS-500 13440 Port Model described in Section 1.1 above shall be
                One hundred thirty-three thousand four hundred thirteen dollars
                ($133,413). The Optional Power Plant includes batteries,
                rectifiers and power board equipment. The batteries are
                provisioned for a four (4) hour reserve period.

December 3, 1996





<PAGE>   34



                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

2.0     INITIAL SYSTEM DMS-500 12480 PORT MODEL (MODEL B-CHICAGO)

        2.1     The following represents the SuperNode equipment that will be
                delivered with the Initial System DMS-500 12480 Port Model
                equipped and wired for 10560 DTEI trunking ports, and equipped
                and wired for 1920 LTEI trunking Ports:

                a)      SuperNode front end, Link Peripheral Processor, Enhanced
                        Network and other common equipment as follows:
                          
                        -       SuperNode equipped with BRISC60 processor, five
                                (5) 96 meg memory cps per plane and SLM III.
                          
                        -       Link Peripheral Processor equipped with eight
                                (8) Link Interface Units, (2) Ethernet Interface
                                Units and wired for thirty six (36) Link
                                Interface Units (LIUs). Four of the eight
                                equipped LIUs will be utilized for interworking.
                          
                        -       V.35 Link Peripheral Processor Interface
                                equipment to support an equipped configuration
                                of eight (8) Interface Units and a wired
                                configuration of thirty six (36) Interface
                                Units.
                          
                        -       Eleven (11) Digital Trunk equipment ISDN Ready
                                (DTEI) frames equipped and wired for 10560
                                trunking ports. Ten thousand eighty (10080)
                                ports are equipped and wired for SS7. Four
                                hundred eighty (480) ports are equipped and
                                wired for PRI functionality. Nine hundred and
                                sixty (960) of the ten thousand eighty SS7 ports
                                are interworking. All DTCIs are equipped with
                                the latest XPM and Universal Tone Receivers for
                                digit collection. Ten thousand eighty (10080)
                                trunks are wired with Special Tone Receivers for
                                Reorigination, and Continuity Tone Detectors for
                                SS7 functionality.
                          
                        -       Two (2) Line Trunk equipment ISDN Ready (LTEI)
                                frames wired and equipped with 1920 SS7 ports.
                          
                        -       Two (2) Integrated Services Module (ISM) frames
                                equipped with DMS-500 service and test circuits
                                providing DMS-500 functionality, as well as six
                                (6) Enhanced Digital Recorded Announcement
                                Machine circuit packs.
                          
                        -       Two (2) Input Output equipment (IOE) frames
                                equipped with:

                                -       One (1) Mag Tape Device

                                -       Four (4) SCSI Disk Drive Units

                                -       Three (3) IOC Shelves

                                -       Three (3) I/O Controllers providing
                                        eight (12) switch interface ports

                                -       Four (4) X.25 Automatic File Transfer
                                        circuit packs
                          
                        -       Two (2) MIS frames equipped with required 500W
                                inverters and terminal block assemblies.
                          
                        -       Two (2) Meridian Cabinet Spare Storage (MCSS)
                                cabinets to house switch spares.
                          
                        -       Two (2) Power Distribution Center (PDC) frames
                                equipped with "A" and "B" feed fuse panels &
                                fuses as required.
                          
                        -       Miscellaneous equipment as follows:

                                -       Two (2) Maintenance Administration
                                        Positions & one set of Furniture

                                -       Five (5) UDS 2440 Modems

                                -       One (1) Norstar Key System

                                -       Two (2) M7310 Feature sets to support
                                        Norstar Key System

                                -       Two (2) RTIF Terminals

                                -       One (1) MAP Printer

                                -       One (1) Helmsman Workstation, CD ROM
                                        Software and Printer
                          
                        -       DSX panels to support a twelve thousand four
                                hundred eighty (12480) port DMS-500 Initial
                                System.

December 3, 1996





<PAGE>   35



                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

        2.1     INITIAL SYSTEM DMS-500 12480 PORT MODEL B CHICAGO CONT.

                b)      Single frame enhanced network to support a twelve
                        thousand four hundred eighty (12480) port DMS-500
                        Initial System.

                c)      Initial System DMS-500 Port Model Standard Features
                        (Base and Optional) as set forth in Section VII of this
                        Schedule A.

                d)      Nortel's standard complement of DMS-500 Initial System
                        spares.

        2.2     INITIAL SYSTEM DMS-500 12480 PORT MODEL B CHICAGO PRICING 
                Refer to Section VI of this Schedule A for detailed Initial
                System Model Pricing.

        2.3     INITIAL SYSTEM DMS-500 12480 PORT MODEL B CHICAGO OPTIONAL POWER
                PLANT PRICING
                The price for Optional Power Plant to support the Initial System
                DMS-500 12480 Port Model described in Section 2.1 above shall be
                one hundred thirty-three thousand four hundred thirteen dollars
                ($133,413). The Optional Power Plant includes batteries,
                rectifiers and power board equipment. The batteries are
                provisioned for a four (4) hour reserve period.

December 3, 1996





<PAGE>   36



                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

3.0     INITIAL SYSTEM DMS-500 14400 PORT MODEL (MODEL C-L.A.)

        3.1     The following represents the SuperNode equipment that will be
                delivered with the Initial System DMS-500 14400 Port Model
                equipped with 12000 and wired for 12480 DTEI trunking ports, and
                equipped and wired for 1920 LTEI trunking ports:

                a)      SuperNode front end, Link Peripheral Processor, Enhanced
                        Network and other common equipment as follows:
                 
                        -       SuperNode equipped with BRISC60 processor, five
                                (5) 96 meg memory cps per plane and SLM III.
                 
                        -       Link Peripheral Processor equipped with eight
                                (8) Link Interface Units, (2) Ethernet Interface
                                Units and wired for thirty six (36) Link
                                Interface Units (LIUs). Four of the eight
                                equipped LIUs will be utilized for interworking.
                 
                        -       V.35 Link Peripheral Processor Interface
                                equipment to support an equipped configuration
                                of eight (8) Interface Units and a wired
                                configuration of thirty six (36) Interface
                                Units.
                 
                        -       Thirteen (13) Digital Trunk equipment ISDN Ready
                                (DTEI) frames equipped with 12000 and wired for
                                12480 total trunking ports. Eleven thousand five
                                hundred and twenty (11520) ports are equipped
                                for SS7 and twelve thousand (12000) ports are
                                wired for SS7. Four hundred eighty (480) ports
                                are equipped and wired for PRI functionality.
                                Nine hundred and sixty (960) ports of the eleven
                                thousand five hundred and twenty (11520)
                                equipped SS7 ports will be used for
                                interworking. AR DTCIs are equipped with the
                                latest XPM and Universal Tone Receivers for
                                digit collection. Eleven thousand five hundred
                                and twenty (11520) trunks are equipped with
                                Special Tone Receivers for Reorigination, and
                                Continuity Tone Detectors for SS7 functionality.
                 
                        -       Two (2) Line Trunk equipment ISDN Ready (LTEI)
                                frames wired and equipped with 1920 SS7 ports.
                 
                        -       Two (2) Integrated Services Module (ISM) frames
                                equipped with DMS-500 service and test circuits
                                providing DMS-500 functionality, as well as, six
                                (6) Enhanced Digital Recorded Announcement
                                Machine circuit packs.
                 
                        -       Two (2) Input Output equipment (IOE) frames
                                equipped with:
                                -  One (1) Mag Tape Device
                                -  Four (4) SCSI Disk Drive Units
                                -  Three (3) IOC Shelves
                                -  Three (3) 1/0 Controllers providing
                                   eight (12) switch interface ports
                                -  Four (4) X.25 Automatic File Transfer
                                   circuit packs

                        -       Two (2) MIS frames equipped with required 500W
                                inverters and block assemblies.
                 
                        -       Two (2) Meridian Cabinet Spare Storage (MCSS)
                                cabinets to house switch spares.
                 
                        -       Two (2) Power Distribution Center (PDC) frames
                                equipped with "A" and "B" feed fuse panels &
                                fuses as required.
                 
                        -       Miscellaneous equipment as follows:

                                -       Two (2) Maintenance Administration
                                        Position & one set of Furniture

                                -       Five (5) UDS 2440 Modems

                                -       One (1) Norstar Key System

                                -       Two (2) M7310 Feature sets to support
                                        Norstar Key System

                                -       Two (2) RTIF Terminals

                                -       One (1) MAP Printer

                                -       One (1) Helmsman Workstation, CD ROM
                                        Software and Printer

December 3, 1996




<PAGE>   37



                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

        3.1     INITIAL SYSTEM DMS-500 14400 PORT MODEL C L.A. CONT.

                        -       DSX panels to support a twelve thousand (12000)
                                equipped port DMS-500 Initial System.

                b)      Single frame enhanced network to support a twelve
                        thousand (12000) equipped port DMS-500 Initial System.

                c)      Initial System DMS-500 Port Model Standard Features
                        (Base and Optional) as set forth in Section VII of this
                        Schedule A.

                d)      Nortel's standard complement of DMS-500 Initial System
                        spares.

        3.2     INITIAL SYSTEM DMS-500 14400 PORT MODEL C LA. PRICING 
                Refer to Section VI of this Schedule A for detailed Initial 
                System Model Pricing.

        3.3     INITIAL SYSTEM DMS-500 14400 PORT MODEL B L.A. OPTIONAL POWER
                PLANT PRICING 
                The price for Optional Power Plant to support the Initial 
                System DMS-500 14400 Port Model described in Section 3.1
                above shall be one hundred thirty-three thousand four hundred
                thirteen dollars ($133,413). The Optional Power Plant includes
                batteries, rectifiers and power board equipment. The batteries
                are provisioned for a four (4) hour reserve period.

December 3, 1996





<PAGE>   38



                                                       MIDCOM PRODUCT ATTACHMENT
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

4.0     INITIAL SYSTEM DMS-250 5760 PORT MODEL (MODEL D-ATLANTA)

        4.1     The following represents the SuperNode equipment that will be
                delivered with the Initial System DMS-250 5760 Port Model
                equipped and wired for 5760 ports:

                a)      SuperNode front end, Link Peripheral Processor, Enhanced
                        Network and other common equipment as follows.
                          
                        -       SuperNode equipped with BRISC60 processor, four
                                (4) 96 meg memory circuit packs per plane and
                                SLM III.
                          
                        -       Link Peripheral Processor equipped with twelve
                                (12) Link Interface Units, (2) Ethernet
                                Interface Units and wired for thirty six (36)
                                Link Interface Units (LIUs).
                          
                        -       V.35 Link Peripheral Processor Interface
                                equipment to support an equipped configuration
                                of twelve (12) Interface Units and a wired
                                configuration of thirty six (36) Interface
                                Units.
                          
                        -       Six (6) Digital Trunk equipment ISDN Ready
                                (DTEI) frames equipped and wired for 5760
                                trunking ports. Five thousand two hundred eighty
                                (5280) ports are equipped for SS7. Four hundred
                                eighty (480) ports are equipped and wired for
                                PRI functionality. All DTCIs are equipped with
                                the latest XPM and Universal Tone Receivers for
                                digit collection. Five thousand two hundred
                                eighty (5280) trunks are equipped with Special
                                Tone Receivers for Reorigination, and Continuity
                                Tone Detectors for SS7 functionality.
                          
                        -       Two (2) Integrated Services Module (ISM) frames
                                equipped with DMS-250 service and test circuits
                                providing DMS-250 functionality, as well as
                                Enhanced Digital Recorded Announcement Machine
                                equipment.
                          
                        -       Two (2) Input Output equipment (IOE) frames
                                equipped with:

                                -       One (1) Mag Tape Device

                                -       Four (4) SCSI Disk Drive Units

                                -       Two (2) IOC Shelves

                                -       Three (3) I/O Controllers providing
                                        twelve (12) switch interface ports

                                -       Two (2) X.25 Automatic File Transfer
                                        circuit packs

                        -       Two (2) MIS frames equipped with required 500W
                                inverters and terminal block assemblies.
                          
                        -       One (1) Meridian Cabinet Spare Storage (MCSS)
                                cabinet to house switch spares.
                          
                        -       Two (2) Power Distribution Center (PDC) frames
                                equipped with "A" and "B" feed fuse panels &
                                fuses as required.
                          
                        -       Miscellaneous equipment as follows:

                                -       Two (2) Maintenance Administration
                                        Position & one set of Furniture

                                -       Five (5) UDS 2440 Modems

                                -       One (1) Norstar Key System

                                -       Two (2) M7310 Feature sets to support
                                        Norstar Key System

                                -       Two (2) RTIF Terminals

                                -       One (1) MAT Printer

                                -       One (1) Helmsman Workstation, CD ROM
                                        Software and Printer

                        -       DSX panels to support a DMS-250 Initial System
                                equipped and wired for five thousand seven
                                hundred sixty (5760) ports.

                b)      Single frame enhanced network to support a DMS-250
                        Initial System equipped and wired for five thousand
                        seven hundred sixty (5760) ports.

December 3, 1996





<PAGE>   39


                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

        4.1     INITIAL SYSTEM DMS-250 5760 PORT MODEL D ATLANTA CONT.

                c)      Initial System DMS-250 5760 Port Model Standard Features
                        (Base and Optional) as set forth in Section IX of this
                        Product Attachment.

                d)      Nortel's standard complement of DMS-250 Initial System
                        spares.

        4.2     INITIAL SYSTEM DMS-250 5760 PORT MODEL D ATLANTA PRICING 
                Refer to Section VI of this Schedule A for detailed Initial 
                System Model Pricing.

        4.3     INITIAL SYSTEM DMS-250 5760 PORT MODEL D ATLANTA OPTIONAL POWER
                PLANT PRICING 
                The price for Optional Power Plant to support the Initial System
                DMS-250 5760 Port Model described in Section 4.1 above shall be
                seventy-four thousand nine hundred ninety dollars ($74,990). The
                Optional Power Plant includes batteries, rectifiers and power
                board equipment. The batteries are provisioned for a four (4)
                hour reserve period.

December 3, 1996

<PAGE>   40

                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

5.0      INITIAL SYSTEM DMS-250 3840 PORT MODEL (MODEL E DALLAS)

         5.1     The following represents the SuperNode equipment that will be
                 delivered with the Initial System DMS-250 3840 Port (Model E
                 Dallas) equipped with 3360 and wired for 3840 ports:

         a)      SuperNode front end, Link Peripheral Processor, Enhanced
                 Network and other common equipment as follows:

                 o        SuperNode equipped with BRISC60 processor, four (4) 96
                          meg memory cps per plane and SLM III.

                 o        Link Peripheral Processor equipped with twelve (12)
                          Link Interface Units, (2) Ethernet Interface Units
                          and wired for thirty six (36) Link Interface Units
                          (LIUs).

                 o        V.35 Link Peripheral Processor Interface equipment to
                          support an equipped configuration of twelve (12) Link
                          Interface Units and a wired configuration of thirty
                          six (36) Interface Units.

                 o        Four (4) Digital Trunk equipment ISDN Ready (DTEI)
                          frames equipped with 3360 and wired for 3840 trunking
                          ports.  Two thousand eight hundred eighty (2880)
                          ports are equipped for SS7.  Four hundred eighty
                          (480) ports are equipped and wired for PRI
                          functionality.  All DTCIs are equipped with the
                          latest XPM and Universal Tone Receivers for digit
                          collection.  Two thousand eight hundred eighty (2880)
                          trunks are equipped with Special Tone Receivers for
                          Reorigination, and Continuity Tone Detectors for SS7
                          functionality.

                 o        Two (2) Integrated Services Module (ISM) frames
                          equipped with DMS-250 service and test circuits
                          providing DMS-250 functionality, as well as Enhanced
                          Digital Recorded Announcement Machine equipment.

                 o        Two (2) Input Output equipment (IOE) frames equipped
                          with:

                          -       One (1) Mag Tape Device

                          -       Four (4) SCSI Disk Drive Units

                          -       Two (2) IOC Shelves

                          -       Three (3) I/O Controllers providing twelve
                                  (12) switch interface ports

                          -       Two (2) X-25 Automatic File Transfer circuit
                                  packs

                 o        Two (2) MIS frames equipped with required 500W
                          inverters and terminal block assemblies.

                 o        One (1) Meridian Cabinet Spare Storage (MCSS) cabinet
                          to house switch spares.

                 o        One (1) Power Distribution Center (PDC) frame equipped
                          with "A" and "B" feed fuse panels & fuses as
                          required.

                 o        Miscellaneous equipment as follows:

                          -       Two (2) Maintenance Administration Positions
                                  & one set of Furniture

                          -       Five (5) UDS 2440 Modems

                          -       One (1) Norstar Key System

                                  Two (2) M7310 Feature sets to support Norstar
                                  Key System

                          -       Two (2) RTIF Terminals

                          -       One (1) MAP Printer

                          -       One (1) Helmsman Workstation, CD ROM Software
                                  and Printer

                 o        DSX panels to support a DMS-250 Initial System
                          equipped for three thousand three hundred sixty (3360)
                          ports

         b)      Single frame enhanced network to support a DMS-250 Initial
                 System equipped for three thousand three hundred sixty (3360)
                 ports.


December 3, 1996
<PAGE>   41
                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEM


5.1      INITIAL SYSTEM DMS-250 3840 PORT (MODEL E DALLAS) CONT.

         c)       Initial System DMS-250 Port Model Standard Features (Base and
                  Optional) as set forth in Section IX of this Product
                  Attachment

         d)       Nortel's standard complement of DMS-250 Initial System spares

5.2      INITIAL SYSTEM DMS-250 3840 PORT (MODEL E DALLAS) PRICING 
         Refer to Section VI of this Schedule A for detailed Initial System 
         Model Pricing.

5.3      INITIAL SYSTEM DMS-250 3840 PORT (MODEL E DALLAS) OPTIONAL POWER PLANT
         PRICING
         The price for Optional Power Plant to support the Initial System
         DMS-250 3840 Port Model described in Section 5.1 above shall be
         seventy-four thousand nine hundred ninety dollars ($74,990).  The
         Optional Power Plant includes batteries, rectifiers and power board
         equipment. The batteries are provisioned for a four (4) hour reserve
         period.

December 3, 1996
<PAGE>   42
                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                               I. INITIAL SYSTEMS

6.0      INITIAL SYSTEM DMS-250 3840 PORT MODEL (MODEL F SEATTLE)

         6.1     The following represents the SuperNode equipment that will be
                 delivered with the Initial System DMS-250 3840 Port (Model F
                 Seattle) equipped with 3360 and wired for 3840 ports:

                  a)      SuperNode front end, Link Peripheral Processor,
                          Enhanced Network and other common equipment as
                          follows:

                          o       SuperNode equipped with BRISC60 processor,
                                  four (4) 96 meg memory cps per plane and SLM
                                  III.

                          o       Link Peripheral Processor equipped with
                                  twelve (12) Link Interface Units, (2)
                                  Ethernet Interface Units and wired for thirty
                                  six (36) Link Interface Units (LIUs)

                          o       V.35 Link Peripheral Processor Interface
                                  equipment to support an equipped
                                  configuration of twelve (12) Link Interface
                                  Units and a wired configuration of thirty six
                                  (36) Interface Units.

                          o       Four (4) Digital Trunk equipment ISDN Ready
                                  (DTEI) frames equipped with 3360 and wired
                                  for 3840 trunking ports.  Two thousand eight
                                  hundred eighty (2880) ports are equipped for
                                  SS7.  Four hundred eighty (480) ports are
                                  equipped and wired for PRI functionality.  AR
                                  DTCIs are equipped with the latest XPM and
                                  Universal Tone Receivers for digit
                                  collection.  Two thousand eight hundred
                                  eighty (2880) trunks are equipped with
                                  Special Tone Receivers for Reorigination, and
                                  Continuity Tone Detectors for SS7
                                  functionality.

                          o       Two (2) Integrated Services Module (ISM)
                                  frames equipped with DMS-250 service and test
                                  circuits providing DMS-250 functionality, as
                                  well as Enhanced Digital Recorded
                                  Announcement Machine equipment.

                          o       Two (2) Input Output equipment (IOE) frames
                                  equipped with:

                                  -    One (1) Mag Tape Device
                                  -    Four (4) SCSI Disk Drive Units
                                  -    Two (2) IOC Shelves
                                  -    Three (3) I/O Controllers providing
                                       twelve (12) switch interface ports
                                  -    Two (2) X.25 Automatic File Transfer
                                       circuit packs

                          o       Two (2) MIS frames equipped with required 500W
                                  inverters and terminal block assemblies.

                          o       One (1) Meridian Cabinet Spare Storage (MCSS)
                                  cabinet to house switch spares.

                          o       One (1) Power Distribution Center (PDC) frame
                                  equipped with "A" and "B" feed fuse panels &
                                  fuses as required.

                          o       Miscellaneous equipment as follows:

                                  -     Two (2) Maintenance Administration
                                        Positions & one set of Furniture
                                  -     Five (5) UDS 2440 Modems
                                  -     One (1) Norstar Key System
                                  -     Two (2) M7310 Feature sets to
                                        support Norstar Key System
                                  -     Two (2) RTIF Terminals
                                  -     One (1) MAP Printer
                                  -     One (1) Helmsman Workstation, CD ROM
                                        Software and Printer

                          o       DSX panels to support a DMS-250 Initial System
                                  equipped for three thousand three hundred
                                  sixty (3360) ports .

         b)      Single frame enhanced network to support a DMS-250 Initial
                 System equipped for three thousand three hundred sixty (3360)
                 ports.

December 3, 1996
<PAGE>   43
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                               I. INITIAL SYSTEMS

         6.1     INITIAL SYSTEM DMS-250 3840 PORT (MODEL F SEATTLE) CONT.

                  c)       Initial System DMS-250 Port Model Standard Features
                           (Base and Optional) as set forth in Section IX of
                           this Product Attachment.

                  d)       Nortel's standard complement of DMS-250 Initial
                           System spares.

         6.2     INITIAL SYSTEM DMS-250 3840 PORT (MODEL F SEATTLE) PRICING
                 Refer to Section VI of this Schedule A for detailed Initial
                 System Model Pricing.

         6.3     INITIAL SYSTEM DMS-250 3840 PORT (MODEL F SEATTLE) OPTIONAL
                 POWER PLANT PRICING
                 The price for Optional Power Plant to support the Initial
                 System DMS-250 3840 Port Model described in Section 5.1 above
                 shall be seventy-four thousand nine hundred ninety dollars
                 ($74,990). The Optional Power Plant includes batteries,
                 rectifiers and power board equipment.  The batteries are
                 provisioned for a four (4) hour reserve period.


December 3, 1996
<PAGE>   44
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         II. LINK PERIPHERAL PROCESSOR

1.0      LINK PERIPHERAL PROCESSOR (LPP)

         Link Peripheral Processor ("LPP") Extensions to a DMS-500 Initial
         System or DMS-250 Initial System Model include the following and shall
         be priced as set forth below:

         1.1     LINK PERIPHERAL PROCESSOR EXTENSIONS

         The price for an LPP Extension to an existing DMS-500 Initial System
         (either equipped with LPP hardware or not equipped with LPP Extension)
         is three hundred thousand dollars ($300,000) for the first thirty-six
         (36) wired and four (4) equipped links ordered.

         The price for an LPP Extension configured as above includes the
         following:

         a)       Link Peripheral Processor Equipment including LIU7s and/or EIU
                  circuit packs;

         b)       Any required NIS expansions;

         c)       V.35 or DS-0A interface equipment to support wired
                  configurations;

         d)       Spare unique circuit packs, if any, per standard Nortel's
                  standard engineering sparing rules;

         1.2      LINK INTERFACE UNIT (LIU) CARDS TO EQUIP A WIRED LPP EXTENSION
                  PRICING

         Refer to Section VI of this Schedule for detailed Link Peripheral
         Processor Optional Equipment Pricing.

         1.3      ETHERNET INTERFACE UNIT (EIU) CARDS TO EQUIP A WIRED LPP
                  EXTENSION

         Refer to Section VI of this Schedule for detailed Link Peripheral
         Processor Optional Equipment Pricing.


December 3, 1996
<PAGE>   45
                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                           II. ADD-ON PORT EXTENSION

1.0      ADD-ON PORT EXTENSION

         1.1     ADD-ON PORT EXTENSION

         In the event Buyer orders ports to be added to any Initial System,
         such ports shall be treated as an Extension to such Initial System
         ("Add-On Port Extension") and takes delivery of such Add-On Port
         Extension before the Turnover Date applicable to such Initial System,
         such Add-on Port Extension shall be ordered at the prices set forth in
         Section VI, 4.0 ("Add-on Port Prices") of this Schedule A, provided
         that Buyer orders such Add-on Port Extension(s) in minimum increments
         of nine hundred sixty (960) ports per Initial System.

         Such Add-On Port Prices include engineering, installation and/or
         testing associated with such Add-On Port Extension.  In the event
         Buyer orders less than the minimum increments of nine hundred sixty
         (960) ports per Initial System, such ports shall be at Nortel's
         then-current prices.

         Refer to Section IV of this Schedule A for a detailed description of
         the equipment included in each Add-On Port extension.


December 3, 1996
<PAGE>   46
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                              IV. EXTENSION PORTS

1.0      DTEI EXTENSION

         1.1     DTEI EXTENSION, FULLY WIRED AND FULLY EQUIPPED ("DTEI
                 EXTENSION")

         A DTEI Extension is configured in minimum increments of 960 ports. Each
         DTEI Extension includes the following: 

         a)       XPM+, or Nortel's then-current common control;

         b)       A quantity of NT6X50AB circuit packs, based on Nortel's
                  engineering rules for the DTEI Extension;

         c)       Either UTR, STR, CTD for DTCs configured for SS7 or PTS
                  capability; or UTR and ISDN pre-processor circuit packs
                  configured for ISDN PRI capability, as ordered by Buyer;

         d)       ENET, MS or processor memory Equipment, as required for the
                  DTEI Extension; 

         e)       DMS-500 or DMS-250 Service/Test Circuits, as required for the
                  DTEI Extension;

         f)       Power Distribution Center (PDC) Equipment, as required for the
                  DTEI Extension; and

         g)       Spare circuit packs, if required, based on Nortel's standard
                  sparing guidelines.

         1.2      DTEI FULLY WIRED AND FULLY EQUIPPED PORT EXTENSION PRICE

         Refer to Section VI, 5.0 ("Extension Port Pricing") for detailed port
         Extension pricing.

         1.3     DTEI EXTENSION OPTIONAL EQUIPMENT

                 1.3.1    DIALABLE WIDEBAND

                 Buyer may order 2 NTAX78AA circuit packs per DTC instead of
                 the NT6X44AA circuit packs with which a DTEI Extension is
                 equipped for an additional price of Five Thousand Dollars
                 ($5,000) per DTC or Ten Thousand Dollars ($10,000) per DTEI
                 frame.

                 1.3.2    ECHO CANCELLATION

                 Buyer may order NT6X50EC circuit packs for a DTEI Extension
                 for installation prior to its Turnover Date for an additional
                 price of Seventy Dollars ($70) per port.



December 3, 1996
<PAGE>   47
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                              IV. EXTENSION PORTS

2.0      LTEI PORT EXTENSIONS

         2.1      LTEI EXTENSION, FULLY WIRED AND FULLY EQUIPPED ("LTEI
                  EXTENSION")

                  An LTEI Extension is configured in minimum increments of 960
                  Ports. Each LTEI Extension includes the following:

         a)       XPM+, or Nortel's then-current common control;

         b)       ENET, NIS or processor memory Equipment, as required for the
                  LTEI Extension;

         c)       DMS-500 Service/Test Circuits, as required for the LTEI
                  Extension;

         d)       Power Distribution Center (PDC) Equipment, as required for the
                  LTEI Extension; and

         e)       Spare circuit packs, if required, based on Nortel's standard
                  sparing guidelines.

         2.2      LTEI FULLY WIRED AND FULLY EQUIPPED PORT EXTENSION PRICE

                  Refer to Section VI, 5.0 ("Extension Port Pricing") for
                  detailed port Extension pricing.



December 3, 1996
<PAGE>   48
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                              IV. EXTENSION PORTS

3.0      ESMA PORT EXTENSIONS

         3.1      ESMA EXTENSION, FULLY WIRED AND FULLY EQUIPPED ("ESMA
                  EXTENSION")

                  An ESMA Extension is configured in minimum increments of 960
                  ports. Each ESMA Extension includes the following:

         a)       Nortel's then-current common control;

         b)       Universal Tone Receivers (UTRs) and ISDN pre-processor circuit
                  packs when ISDN PRI capability be required;

         c)       ENET, MS or processor memory Equipment, as required for the
                  ESMA Extension;

         d)       DMS-500 Service/Test Circuits, as required for the ESMA
                  Extension;

         e)       Power Distribution Center (PDC) Equipment, as required for the
                  ESMA Extension;

         f)       Optional Class Modem Resource circuit packs (N6X78AA), one (1)
                  per ESMA module; and

         g)       Spare circuit packs, if required, based on Nortel's standard
                  sparing guidelines.


         3.2      ESMA FULLY WIRED AND FULLY EQUIPPED PORT EXTENSION PRICE

                  Refer to Section VI, 5.0 ("Extension Port Pricing") for
                  detailed port Extension pricing.


December 3, 1996
<PAGE>   49
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         V. DMS-250 TO DMS-500 UPGRADE

1.0      DMS-250 TO DMS-500 SYSTEM UPGRADE

         1.1     DMS-250 TO DMS-500 SYSTEM UPGRADE INCLUDES:

                 As used in this Product Attachment, the DMS-250 to DMS-500
                 System Upgrade shall consists of the following configuration
                 of Equipment and Software:

                 a)       DMS-500 Common and Peripheral equipment as follows:

                          o       One (1) DTEI frame equipped and wired for 960
                                  SS7 Interworking Ports.

                          o       Two (2) LTEI frames equipped and wired for
                                  1920 Trunking Ports.

                          o       ENET Equipment as required for the DMS250 to
                                  DMS-500 System Upgrade.

                          o       One (1) Integrated Services Module (ISME)
                                  frame equipped with DMS-100 service circuits.
                                  (DMS-250 service circuits already exist).

                          o       Two (2) SCSI Disk Drive Units.

                          o       Four X.25 Automatic File Transfer circuit
                                  packs.

                          o       Two (2) 96mb memory circuit packs, as
                                  required, to support the additional DMS-500
                                  Base Software being added.

                          o       Two (2) X.25 Automatic FileTransfer circuit
                                  packs

                          o       Four (4) Link Interface Units to be
                                  engineered in existing LPP frame.  The four
                                  (4) link interface units are being provided
                                  for interworking.

                          o       Two (2) Ethernet Interface Units (EIUs)

                          o       DMS-500 Base Software.

                          o       Nortel's standard complement of DMS-500
                                  system spares for the above defined
                                  equipment.  Spares are only being provided
                                  for unique circuit packs engineered for this
                                  DMS-250 to DMS-500 System Upgrade.

         1.2      DMS-250 TO DMS-500 UPGRADE PRICING

                  Refer to Section VI, 8.0 ("DMS-250 to DMS-500 Upgrade
                  Pricing") for detailed Upgrade pricing.



December 3, 1996
<PAGE>   50
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                    VI.  DMS-250 AND DMS-500 PRICING MATRIX


1.0      COMMITMENT LEVEL TABLE

         Commitment Level

<TABLE>
         <S>     <C>
         1       $0-  $9,999,999M
         2       $10-$19,999,999M
         3       $20-$29,999,999M
         4       $30-$39,999,999M
</TABLE>

2.0      PRICE MATRIX FOR INITIAL SYSTEM MODELS

<TABLE>
<CAPTION>
Commitment       NYC-500          Chi-500          LA-500           Atl. 250
   Level         Model A          Model B          Model C          Model D
----------       -------          -------          -------          -------
       <S>       <C>              <C>              <C>              <C>
       1         $ 3,019,875      $2,961,315       $3,136,995       $1,850,220
       2         $ 2,819,500      $2,763,820       $2,930,860       $1,727,160
       3         $ 2,607,125      $2,554,805       $2,711,765       $1,598,340
       4         $ 2,394,750      $2,345,790       $2,492,670       $1,469,520

                 Dls-250          Seattle-250
                 Model E          Model F
                 -------          -------
                 $1,557,420       $1,557,420
                 $1,448,760       $1,448,760
                 $1,336,740       $1,336,740
                 $1,224,720       $1,224,720
</TABLE>

NOTES:

Power for the above Systems is not included in the price and should be added
per Section I.1.0 through 6.0 of this Schedule A.

3.0      LINK PERIPHERAL PROCESSOR PRICING

<TABLE>
<CAPTION>
Commitment
   Level         LIU Addition          EIU Addition
   ------        ------------          ------------
       <S>       <C>                       <C>
       1         $ 11,000                  $ 14,000
       2         $ 10,500                  $ 13,500
       3         $ 10,000                  $ 12,500
       4         $  9,500                  $ 11,500
</TABLE>


December 3, 1996
<PAGE>   51
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                     VI. DMS-250 AND DMS-500 PRICING MATRIX

4.0    ADD-ON PORT PRICES (PER EACH PORT)

<TABLE>
<CAPTION>
      Commitment
        Level       DTC7/LTC       DTC1 LD       DTCI Local        ESMA
        -----       --------       -------       ----------        ----
          <S>        <C>             <C>           <C>            <C>
          1          $ 136           $ 154         $ 278          $ 168
          2          $ 129           $ 146         $ 264          $ 160
          3          $ 123           $ 139         $ 250          $ 151
          4          $ 116           $ 131         $ 236          $ 143
</TABLE>

5.0    EXTENSION PORT PRICING (PER EACH PORT)

<TABLE>
<CAPTION>
     Commitment
        Level       DTC7/LTC       DTCI LD       DTCI Local        ESMA
        -----       --------       -------       ----------        ----
          <S>         <C>           <C>            <C>             <C>
          1           $ 204         $ 240          $ 417           $ 252
          2           $ 194         $ 228          $ 396           $ 239
          3           $ 184         $ 216          $ 375           $ 226
          4           $ 174         $ 204          $ 354           $ 214
</TABLE>

6.0    Discount Matrix - Initial System Optional Software License
       Fees (Pre-Turnover)

       In the event Buyer elects to license during the Product Attachment Term,
       Optional Software, listed in Sections VIII and X of this Schedule A,
       prior to the Turnover Date associated with an Initial System on which
       such Optional Software is to be installed, the Software Discount
       associated with the applicable Commitment Level set forth below shall be
       applied to the Optional Software License Fees listed in Sections VIII
       and X of this Schedule A.

<TABLE>
<CAPTION>
                                        Software
        Commitment Level                Discount
        ----------------                --------
              <S>                         <C>
              1                            65%
              2                            70%
              3                            75%
              4                            80%
</TABLE>

7.0    DISCOUNT MATRIX - INITIAL SYSTEM OPTIONAL SOFTWARE LICENSE FEES
       (POSTTURNOVER) 

       In the event Buyer elects to license during the Product Attachment Term,
       Optional Software listed in Sections VIII and X of this Schedule A,
       during the twelve (12) month period following the Turnover Date
       associated with the Initial System on which such Optional Software is to
       be installed, the Software Discount associated with the applicable
       Commitment Level set forth below shall be applied to the Optional
       Software License Fees listed in, as applicable, Sections VIII and X of
       this Schedule A, during the term of the contract.

<TABLE>
<CAPTION>
                                        Software
        Commitment Level                Discount
        ----------------                --------
              <S>                         <C>
              1                            30%
              2                            35%
              3                            40%
              4                            45%
</TABLE>



December 3, 1996
<PAGE>   52
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                     VI. DMS-250 AND DMS-500 PRICING MATRIX

8.0      DMS-250 TO DMS-500 UPGRADE PRICING

         Nortel shall make available to Buyer a DMS-250 to DMS-500 Software and
         Equipment upgrade to include those items listed in Section V of this
         Schedule A, for the prices set forth below:

<TABLE>
<CAPTION>
              Commitment               DMS-250 to DMS-500
                Level                    Upgrade Price
                -----                    -------------
                  <S>                      <C>
                  1                        $ 571,875
                  2                        $ 518,750
                  3                        $ 465,625
                  4                        $ 412,500
</TABLE>

9.0    DMS-250 IEC02 TO UCS05 SOFTWARE UPGRADE PRICING

       Nortel shall make available to Buyer a DMS-250 IEC02 to UCS05 Software
       Upgrade, when Generally Available, at the price set forth below.

<TABLE>
<CAPTION>
  Commitment
    Level                      Upgrade Price
    -----                      -------------
     <S>                        <C>
     1-4                        $ 65,000
</TABLE>



December 3, 1996
<PAGE>   53
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII DMS-500 STANDARD FEATURES

1. DMS-500 INITIAL SYSTEM STANDARD FEATURES

1.1      DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES

         The following represents the DMS-500 LLT0B005 base and optional
         Software packages that are included in the price of a DMS-500 Initial
         System Model A, Model B and Model C, ("Standard Features").  The
         following is a list of Software only included in the Schedule A
         Initial System(s); this list does not include any/all required
         Equipment to provide feature functionality.

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
--------------     -----------     -----------
<S>                <C>             <C>
UCS0005                            UCS TANDEM SERVICES BASE
                   NTX292BA        Enhanced Security-without Password Encryption  
                   NTX702BB        DMS-500 Universal Master Package (UCS)         
                   NTXOOOAA        Bilge                                          
                   NTX001AA        Common Basic                                   
                   NTX048AA        Synchronization                                
                   NTX051AA        Automatic Trunk Testing                        
                   NTX053AA        Maintenance Assistance Package                 
                   NTX055AA        Trunk Test Position (TTP)                      
                   NTX055AB        TTP Digit Verification                         
                   NTX055AC        TIP Transmission Measurement                   
                   NTX056AA        Enhanced Administration                        
                   NTX060AB        Network Management                             
                   NTX060BB        Network Management - Enhanced                  
                   NTX072AA        International Direct Distance Dialing (IDDD)   
                   NTX074AA        Disk Data Storage Storage System               
                   NTX085AA        Traffic Separation Peg Count                   
                   NTX087AA        Traffic Separation Usage                       
                   NTX088AA        Traffic Separation Report                      
                   NTX099AA        Operational Measurements Enhancements          
                   NTX122AA        OM Call Attempts Summary                       
                   NTX136AA        Automatic Transmission Measuring System        
                   NTX202AA        DMS-250 Operational Measurements on Tape       
                   NTX203AA        DMS-250 104 Testlines                          
                   NTX220BA        DMS-250 Base Package (Type II)                 
                   NTX221BA        DMS-250 Call Detail Recording (Type II) Billing
                   NTX222BA        DMS-250 Call Processing (Type II)              
                   NTX227BA        DMS,250 Time Of Day Routing                    
                   NTX228BA        DMS-250 DCM Channel Unit Cross Reference       
                   NTX230BA        DMS-250 Speed Numbers (Public/Private)         
                   NTX231BA        DMS-250 Incoming Exclusion                     
                   NTX234BA        DMS-250 Authcodes (Type II)                    
                   NTX235BA        DMS-250 Restricted Usage By Date and Time      
                   NTX236BA        DMIS-250 Alternate Trunk Group Treatments      
                   NTX239BA        DMS-250 Translation Verification               
                   NTX244AB        Enhanced Sequential Trunk Hunting              
                   NTX269AA        Universal Tone Receivers                       
                   NTX270AA        New Peripheral Maintenance Package             
                   NTX291AA        Enhanced Real Time Indicator                   
                   NTX321BA        DMS-500 Generic Offnet Access Trunks (FG-B)    
</TABLE>

December 3, 1996
<PAGE>   54
                                                       MIDCOM Product Attachment
                                   Schedule A

                      VII.      DMS-500 Standard Features

1.1    DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
--------------     -----------     -----------
<S>                <C>             <C>
UCS00005                           UCS TANDEM SERVICES BASE                     
                   NTX702BB        DMS-250 Universal Master Package (UCS)       
                   NTX342BA        DMS-250 Equal Access Base Package (FG-D)     
                   NTX343BA        DMS-250 Equal Access (Type II) - ANI Scrn    
                   NTX347AA        DMS, Base Data Communication Software        
                   NTX351BA        DMS-250 Automatic Trunk Routining
                   NTX445AB        Operational Measurement Selective Output     
                   NTX738AC        Switch Performance Monitoring System (SPMS)  
                   NTX801AA        Toll Features I                              
                   NTX827AA        New Peripherals Performance Measurements     
                   NTX903AA        Transmission Measurements                    
                   NTXA11AA        Patch Administration & Downloading via X.25  
                   NTXG22AA        DMS-250 UCS Outgoing FG-D Enhancements       
                   NTXG24AA        DMS-250 Integrated Echo Cancellor            
                   NTXJ35AA        Maintenance Managers Report                  
                   NTXL02AA        DMS-250 UCS Dialing Plan Enhancements        
                   NTXL05AA        DMS-250 Roaming PINs                         
                   NTXL79AA        DMS-250 XPM+ for DTC7/DTCI                   
                   NTXR34AB        XPM Plus Basic                               
                   NTXR42AA        Firmware Downloading                         
                   NTXG18AA        DMS-250 Safe Store TAP (X.25 Applications)   
                   NTXM70AA        UCS Tandem Services Base                     
                   NTX065AA        Service Analysis                             
                   NTX142AA        DS-1 64 KBPS Clear                           
                   NTX143AA        DS-1 ESF                                     
                   NTX167AB        CCS7 Trunk Signalling                        
                   NTX226BA        DMS-250 ATB by NPA Using Operational Meas.   
                   NTX232BA        DMS-250 ATB by NPA Using Logs                
                   NTX233BA        DMS-250 Off Hook Queuing                     
                   NTX237AA        DMS-250 Nailed Up Connections                
                   NTX340BA        DMS-250 Adaptive Routing                     
                   NTX346BA        DMS-250 Intra Lata Intra State Screening     
                   NTX361BA        DMS-250 CCS7 IMTS                            
                   NTX368BA        DMS-250 Multiple Authcode Sets               
                   NTX437AA        Random Conditional Routing                   
                   NTX550AA        CCS7 Transaction Service Support             
                   NTX836AA        LPP V.35 Subrate Links                       
                   NTX839AB        LPP Enhanced Maintenance and Bert            
                   NTX840AA        LIU7 Gateway Message Screening               
                   NTX882AA        Bit Error Ratio Indicator for Toll Switches  
                   NTX883AA        Inter Office Trunk Bit Error Rate            
                   NTX885AB        Switch Pat Diagnostics                       
                   NTX945AA        MS Base Link Maintenance                     
                   NTXA67AA        Extended XPM Diagnostics                     
                   NTXE01AA        Enhanced Network Basic (ENET)                
</TABLE>



December 3, 1996
<PAGE>   55
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

1.1     DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
--------------     -----------     -----------
<S>                <C>             <C>
UCS00005                           UCS TANDEM SERVICES BASE                     
                   NTXM70AA        UCS Tandem Services Base Cont.               
                   NTXE32AA        CCS7 Preventative Cyclical Retransmission    
                   NTXE65AA        MPC X25 Interface                          
                   NTXE98AA        High Speed MPC                               
                   NTXF05AA        Ethernet Interface Unit                      
                   NTXF19AA        TCP/IP Protocols                             
                   NTCF20AA        LMS on LPP                                   
                   NTXF71AB        SuperNode Enhanced Messaging                 
                   NTXG10AA        DMS-250 CNS CCITT 1984 X.25 Datacom          
                   NTXG13AA        DMS Base Data Access Interface Session       
                   NTXG18BA        DMS-250 Safe Store Tap                       
                   NTXG20AA        DMS-250 SS7 FG-D                             
                   NTXG28AA        DMS-250 Enhanced COS Screening               
                   NTXG34AA        DMS-250 Trunk Group and CLLI name analysis  
                   NTXG35AA        DMS-250 Paystation Pretranslator             
                   NTXG42AA        DMS-250 SS7 IMT Terminations to DTU          
                   NTXG46AA        DMS-250 Direct Termination Service           
                   NTXG49AA        DMS-250 UCS SS7 UCP (Base ISUP)              
                   NTXJ40AA        LIU7 Gateway Verification Tools             
                   NTXJ41AA        CCS7 Test Tools                              
                   NTXJ44AA        SLM File System                              
                   NTXJ94AA        Mandatory Parallel AMA                       
                   NTXL01AB        DMS-250 UCS, Account Code Screening Enh.     
                   NTXL03AA        DMS-250 UCS to USP ISUP Interworking         
                   NTXL04AA        DMS-250 UCS SS7 Intra/Inter Networking       
                   NTXL08AA        DMS-250 UCS X.25 Transport                   
                   NTXL09AA        DMS-250 UCS PRA                              
                   NTXL11AA        DMS-250 UCS to MCI ISUP Interworking         
                   NTXL124A        DMS-250 UCS to FGD ISUP Interworking         
                   NTXL14AA        DMS-250 UCS International Partitioning       
                   NTXL47AA        DMS-250 Lower Layer Compatibility            
                   NTXN16AA        Enhanced Dram                                
                   NTXN18AA        FBUS LIU Base                                
                   NTXN19AA        LIU7 for LPP Based CCS7 Applications         
                   NTXN68AA        XPM Broadcast Patching                       
                   NTXN83AA        LIS Common                                   
                   NTXP10AA        Network Module Software                      
                   NTXP13AA        Enet Switch Path Diagnostics                 
                   NTXP14AA        Dirp Parallel Storage Size Increase          
                   NTXQ51AA        MS SR512 Lis Controller                      
                   NTXR70AA        CM Base for OPC                              
                   NTXR72AA        CCS7 MTP/SCCP for LPP                      
                   NTXS11AA        File Transfer Protocol                       
</TABLE>


December 3, 1996
<PAGE>   56
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

1.1    DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
----------         -----------     -----------
<S>                <C>             <C>
UCS00005                           UCS TANDEM SERVICES BASE
                   NTXM70AA        UCS Tandem Services Base Cont.

                   NTXX26AA        DMS-250 UCS X-25 Data Transport
                                     Enhancements
                   NTXX30AA        UCS Enhanced Dialing Plan Phase II
                   NTXX32AA        Enhanced PANI on UCS
                   NTXX42AA        Disallow Reorigination on EANT FG-D
                                     Trunks
DMS-500 LOCAL
BAS00001                           Base COOK
                   NTX243AA        AMA Teleprocessing System
BAS00002                           Base ANI
                   NTX986AA        Automatic Number Identification with AMA
BAS00003                           Base Generic
                   NTX000AA        Bilge
                   NTX001AA        Common Basic
                   NTX006AA        Business Lines
                   NTX007AB        PBX Interface I
                   NTX008AB        PBX Interface II
                   NTX019AA        Civic Services
                   NTX020AC        Vert. Services (POTS)
                   NTX021AA        Remote Call Forward
                   NTX029AA        Direct Dialing Overseas, Toll
                   NTX041AB        CCS7 MTP/SCCP
                   NTX042AA        Local AMA
                   NTX043AA        Local CDR
                   NTX044AA        CAMA
                   NTX045AA        Usage Sen Pricing
                   NTX048AA        Synchronization
                   NTX048AB        Synchronization Censium Master Clock
                   NTX048BA        Synchronization Stratum 3
                   NTX048CA        Synchronization Stratum 2
                   NTX049AC        Circle Digit ID
                   NTX049AD        Sgl Pty Rev Call
                   NTX049AE        North Elec ANI Frmt
                   NTX049AG        ITT ANI Format
                   NTX049AH        Come Again Signaling
                   NTX049AL        Time and Temperature
                   NTX051AA        Automatic Trunk Testing
                   NTX052AB        ROTL
                   NTX053AA        Maintenance Assistance Package
                   NTX054AA        Line Test Position (LTP)
                   NTX055AA        Trunk Test Position (TTP)
                   NTX055AB        TTP Digit Verification
                   NTX055AC        TTP Transmission Measurement
                   NTX055BA        RONI Trunk Testing
                   NTX056AA        Enhanced Administration
                   NTX059AB        Poll OM Data via Dpk
</TABLE>

December 3, 1996
<PAGE>   57
                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

1.1    DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
----------         ------------    -----------
<S>                <C>             <C>
BAS0003 Cont.
                   NTX060AB        Network Management
                   NTX060BB        Enhanced Network Management
                   NTX063AA        Echo Suppresser
                   NTX065AA        Service Analysis
                   NTX066AB        Bilingual Interface
                   NTX074AA        Disk Data Storage System
                   NTX076AA        AMA Enhanced
                   NTX077AA        Online Peripheral Software
                   NTX080AA        LAMA Enhanced
                   NTX080BA        Term Call Blng
                   NTX082AA        Sub Line Usage
                   NTX083AA        Feature Group A
                   NTX085AA        Traffic Sep Peg Count
                   NTX087AA        Traffic Sep Usage
                   NTX088AA        Traffic Sep Report
                   NTX089AA        Enhanced Coin Services
                   NTX090AA        Coin Services
                   NTX094AA        Digital Sub Svcs
                   NTX098AA        Bellcore CAMA Format
                   NTX099AA        OM Enhancements
                   NTX120AA        Office Hardware Inv. Pkg
                   NTX121AA        Overlap Outpulsing (Trunk to Trunk)
                   NTX122AA        OM Call Attempts Summary
                   NTX129AA        2Way Opr Office Trunk
                   NTX136AA        Automatic Transmission Measuring System
                   NTX139AA        Revert Pulse Dig Ln
                   NTX142AA        DS-1 64 Kbps Clear
                   NTX143AA        DS-1 ESF
                   NTX159AA        Bellcore LAMA Format
                   NTX160AA        Multiunit Msg Rt Svc
                   NTX174AA        Automatic Identification of Outward Dialing
                   NTX190AA        FGB, AMA Tandem NT Fmt
                   NTX192AA        4X Opr Bell Format ANI
                   NTX193AA        4X Opr AMR5 Format ANI
                   NTX195AA        Mech Loop Test Interface
                   NTX196AA        Clng No Announcement
                   NTX202AA        DMS-500 Operational Measurements
                   NTX206AA        Unauthorized Digit Service Detection
                   NTX209AB        FGB AMA End AT&T Format
                   NTX210AA        No 2 SCC Interface
                   NTX211AB        FGB, AMA. Tandem AT&T Format
                   NTX215AA        SES No 2 Interface
                   NTX218AA        1A/1B EADAS I/F
                   NTX227AA        DMS-500 Time of Day Routing
                   NTX237AA        DMS-500 Conference Calling
</TABLE>

December 3, 1996
<PAGE>   58
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES


1.1      DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
----------         ------------    -----------
<S>                <C>             <C>
BAS0003 Cont.
                   NTX244AB        Enhanced Sequential Trunk Hunting    
                   NTX268AA        FGB AMA End NT Format                
                   NTX269AA        Uuniversal Tone Receivers            
                   NTX270AA        New Peripheral Maint. Package        
                   NTX272AA        XPM Maintenance                      
                   NTX273AA        Multi Protocol Controller BX.25      
                   NTX274AA        DTC 30 Carrier Maintenance           
                   NTX277AA        Dialable Line Ckt ID                 
                   NTX290AA        Tanderming Supervision and Treatment 
                   NTX291AA        Enhanced Real Time Indicator         
                   NTX292AB        Enhanced Security with password      
                   NTX293AA        Enhanced Security Package II         
                   NTX385AA        OM Thresholding and Alarms           
                   NTX395AA        Remote MB via Scan Point             
                   NTX437AA        Random Conditional Routing           
                   NTX445AB        OM Selective Output                  
                   NTX445AB        1A EADAS Network Mgmt.               
                   NTX479AA        Intl. Univ. Tone ACUR Support      
                   NTX488AA        International Tune of Day Routing    
                   NTX558AA        CC EO DP/DTMF Genrtn                 
                   NTX559AA        CC SSP DP/DTMF Sprtn                 
                   NTX560AB        NOP Generic RO Service               
                   NTX562AA        NOS Data Collection                  
                   NTX712AA        CCS7 Data Port                       
                   NTX721AA        Interval Announcement Response Capability    
                   NTX730AA        Multilink, ASCII Driver                      
                   NTX738AC        Switch Performance Monitoring System 
                   NTX801AA        Toll Features I                      
                   NTX802AA        Toll Features II                     
                   NTX806AA        Enhanced Call FWD (POTS)             
                   NTX807AB        Call Waiting (POTS)                  
                   NTX808AA        Enhanced TWC (POTS)                  
                   NTX812AA        Centralized MAP                      
                   NTX813AA        Centralized Alarms                   
                   NTX827AA        New Peripherals Performance Measurements   
                   NTX881AC        Sw Bit Error Ratio Maintenance             
                   NTX882AA        Bit Error Ratio Indicator for Toll Switches
                   NTX883AA        Interoffice Trk Bit Error Ratio Testing    
                   NTX885AB        Switch Path Diagnostics                    
                   NTX892AA        MPC Multilink Management                   
                   NTX901AA        Local Features II
                   NTX902AA        Local Features II
                   NTX903AA        Transmission Measurements                  
                   NTX925AA        ISC Time of Day and Percentage Routing     
</TABLE>


December 3, 1996
<PAGE>   59
                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

1.1   DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
----------         ------------    -----------
<S>                <C>             <C>
BAS0003 Cont.
                   NTX940AA        CM Bilge                                 
                   NTX941AA        CMCommcn                                 
                   NTX942AB        DMS SuperNode System Load Module         
                   NTX944AA        Base Mode Maintenance                    
                   NTX945AA        MS Base Link Maintenance                 
                   NTX950AA        MS Bilge                                 
                   NTX951AA        MS Common                                
                   NTX987AA        Fiber Mtc Basic Mode                     
                   NTX989AA        Cxr Access Code Blocking                 
                   NTXA11AA        Patch Administration and Downloading     
                   NTXA15AA        Call Progress Comfort Tones              
                   NTXA67AA        Extended XPM Diagnostics                   
                   NTXA89AA        SMDR Time Dump for BNM                 
                   NTXB01AA        Intl Traffic Separation Report           
                   NTXB74AA        EBI A-Law                                
                   NTXB91AA        411 Rec on Mag Tape                      
                   NTXE01AA        Enhanced Network Basic                   
                   NTXE30AA        CCS7 Signaling Link Enhanced Maint MSB7  
                   NTXE54AA        System Load Module II                    
                   NTXE65AA        MPC X.25 Interface                       
                   NTXE98AA        High Speed MPC                           
                   NTXF04AA        File Processor                           
                   NTXF05AA        Ethernet Interface Unit (EIU)            
                   NTXF06AA        Application Processor Base               
                   NTXF07AA        Fault Tolerant File System               
                   NTXF19AA        TCP/IP Protocols                         
                   NTXF20AA        LMS on LPP                               
                   NTXF26AA        Synchronization BITS Composite Master    
                   NTXF27AA        Synchronization Cesium Loran CMA         
                   NTXF46AA        Base SCM Access                          
                   NTXF71AB        SuperNode Enhanced Messaging             
                   NTXG13AA        DMS Base Data Access Interface Session (DAIS)
                   NTXG18BA        DMS-500 Safe Store Tap                      
                   NTXH10AA        PCM-30 Maintenance Enhancements             
                   NTXH11AA        M20 Enhancements                            
                   NTXH51AA        PCM30 LGO/DTCO Spt.                         
                   NTXH62AA        Perform on PLGC/PDTC/PRCC                   
                   NTXH63AA        DMS-300 ANSI ISUP to CCITT TUP Interworking 
                   NTXH77AA        Channelized Access on LPP/Lis               
                   NTXH91AA        DMS-300 Real Time File Transfer             
                   NTXJ35AA        Maintenance Managers Report                 
                   NTXJ44AA        SLM File System                             
                   NTXJ58AA        Cancel Call Waiting                         
                   NTXJ94AA        Mandatory Parallel AMA                      
</TABLE>

December 3, 1996

<PAGE>   60

                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

1.1    DMS-500 Initial System Base and Optional Software Packages (Cont.)

<TABLE>
<CAPTION>
FEATURE/
MASTER MG          S/W PACKAGE     DESCRIPTION
---------          -----------     -----------
<S>                <C>             <C>
BAS0003 Cont.
                   NTXP17AA        DMS-500 Billing Server Base
                   NTXP72AA        ENET 16K Configuration
                   NTXP81AA        Remote Act of LLC
                   NTXP90AA        Meridian SuperNode Option 201
                   NTXP94AA        FITS Disk Shadowing
                   NTXP97AA        IEM Basic Event Consolidation
                   NTXQ32AA        Digital Audio Tape (DAT) Storage
                   NTXQ51AA        MS SR512 LIS Controller
                   NTXQ52AA        Support for MS Resident LIS Controller
                   NTXQ96AA        IEM Base Phase III
                   NTXR21AA        EADAS Hardware Inventory Control
                   NTXR34AB        XPM Plus
                   NTXR42AA        Firmware Downloading
                   NTXR46AA        Robustness Enhancements
                   NTXR70AA        CM Base for DMS SuperNode Data Manager
                   NTXS00AA        Interchangeable NPA
                   NTXS07AA        Telco Defined Login Banner
                   NTXS11AA        File Transfer Protocol (DARPA)
                   NTXS29AA        APU Maintenance
                   NTXS72AA        Software Support for EDRAM Uploading
                   NTXVOOAA        DN Screening Database - Base
                   NTXV11AA        PCM-30 Digital Trunk controller Interface
                   NTXV18AA        Message Transfer Part (MTP)
                   NTXV20AA        DMS-100 Automatic File Transfer (AFT)
                   NTXV26AA        DN Screen Enhancement III
                   NTXW00AA        World Line Card - Basic
                   NTXX98AA        DMS-MTX MNP
BAS00004                           Base OA&M
                   NTXN31AA        Operations System Interface Enhancement
BAS00007                           Base Logs
                   NTXQ95AA        Line Log Reduction
BASE0001                           Base 0001
                   NTX243AA        AMA Teleprocessing
BASE0006                           Base SN Series 60 Processor
                   NTXR61AA        SN SR60 Processor
TEL00001                           Telecom Layer
                                   Refer to "BAS00003" above
BAS00020                           Base Flexible Bellcore AMA
                   NTX737AB        Flexible Bellcore AMA
BAS00028                           Base DPP
                   NTXF14AA        High Capacity DPP
</TABLE>

December 3, 1996

<PAGE>   61
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

1.1    DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
----------         -----------     -----------
<S>                <C>             <C>
LOC00001                           Local Services
                   NTX297AA        Bridged Services
SS700001                           SS7 Trunk Signalling
                   NTX167AB        SS7 Trunk Signaling Base
                   NTX875AA        SS7 Mass Trunk Conversion
                   NTXE66AA        SS7 ISUP Option Controls
                   NTXJ54AA        SS7 FGD MF/SS7 Interworking
                   NTXP48AA        SS7 2-Wire Emulation
UDD00001                           UDD Services
                   NTX072AA        US DDD International DDD
                   NTX735AA        U.S. DDD Flexible Automatic Number Ident.
WLC00001                           World Line Card Enhanced
                   NTXW03AA        Over Voltage Reporting
                   NTXW20AA        North American 900 +2 Type A Template
                   NTXW21AA        North American 900 +2 Type B Template
                   NTXD26AA        SuperNode Series 60 Processor Master
EQA00006                           EQA C71SUP IRLTA, CNTN EAEO
EQA00008                           EQA POTS IRALATA PIC EAEO
EQA00009                           EQA IBN IRALATA PIC EAEO
ENS00005                           ENS ENHANCED 911
ENS00001                           ENS LDT PSAP
MDC00004                           MODC CLASS ON MDC
MDC00008                           MDC MBS STANDARD
MDC00009                           MDCPRO
MDC00010                           MDC CLASS ON MDC/MPV II
MDC00035                           MDC TEEN SERVICE
                   MDC00035-Vl     MDC Teen Svc per 100 Line Fee
</TABLE>

Right to Use Software License for the following packages is based on the number
of LGCs (Local) ot DTCs (Long Distance) required to support equal access
functionality.  Software Right to Use for these packages is provided as part of
the DMS-500 Initial System price and DMS-250 to DMS-500 upgrade price based on
the equipment configurations as defined in this Schedule A, Sections I and V.
Extensions past the equipment engineered with the DMS-250 to DMS-500 Upgrade
and the DMS-500 Initial System would incur additional Right to Use Software
License fees as defined in below:
<TABLE>
<S>                  <C>                                          <C>
EQA00001             EQUAL ACCESS LOCAL
                     EQA00001-VI Equal Access Local per LGC fee    $ 4,800
EQA00002             EQUAL ACCESS TOLL
                     EQA00002-VI EA Toll per DTC fee               $ 4,800
</TABLE>

December 3, 1996

<PAGE>   62
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

Right to Use Software License for the following packages is based on a per line
basis, based on the type of line (Class, Centrex or BRI) that is ordered.
Equipment engineered, furnished and install in addition to that which is
included with the DMS-250 to DMS-500 Upgrade configurations as defined in this
Schedule A, Section V, subparagraph 1.0 and the DMS-500 Initial System are
subject to the additional Right to Use Software License fees as defined below:

Centrex:       The Software Right to Use Fee for the following Centrex Software
packages on a per line charge basis is $14 for Extensions and $9 for Initial
Systems:

<TABLE>
<S>              <C>
MDC00001         MERIDIAN DIGITAL CENTREX MIN.
MDC00003         MDC-MDC STANDARD
MDIC00007        MDC MBS MINIMUM
</TABLE>

BRI:     The Software Right to Use Fee for the following BRI Software packages
on a per line charge basis is $300 for Extensions and $250 for Initial Systems:

<TABLE>
<S>              <C>
NIO00007         NIO ISDN BASE (REQD ALL ISDN)
NIO00008         NIO NI-1 BRI
NIO00010         NIO NI-1 PACKET SERVICES
</TABLE>

CLASS          The Software Right to Use Fee for the following CLASS Software
packages on a per line charge basis is $29 for Extensions and $19 for
Initial Systems:.

<TABLE>
<S>              <C>
RES00003         RES DISPLAY FUNCT. & PRIVACY
RES00005         RES NON-DISPLAY SERVICES
RES00006         RES SERVICE ENABLER
RES00021         RES ANONYMOUS CALLER REJECTION
RES00030         RES CUSTOMER ORIGINATED TRACE
RES00032         RES SELECTIVE CALL FORWARDING
RES00033         RES SELECTIVE CALL REJECTION
RES00034         RES DISTINCTIVE RINGING/CALL WAITING
RES00035         RES SELECTIVE CALL ACCEPTANCE
</TABLE>



December 3, 1996
<PAGE>   63

                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

1.1     DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PACKAGE     S/W PACKAGE     DESCRIPTION
--------------     -----------     -----------
<S>                <C>             <C>                               <C>
NTS00005                           EQUAL ACCESS 800
NTS00012                           NTS EXTENDED CAPABILITY
NIO00022                           NIO ISDN PRI BASE
                   NIO00022-VI     NIO ISDN PRI Base per PRI link    $ 2,000
RES00002                           RES ADV. CUSTOM CALLING FEAT.
                   RES00002-VI     RES ACCF per 100 lines            $ 2,500
RES00004                           RES INTERFACE FUNCTIONALITY
                   RES00004-VI     RES I/F Funct. per 25 links       $25,000
RES00017                           RES TEEN SERVICE
RES00019                           RES CALL FWD REMOTE ACTIVATION

N00R00001                          N00 ROUTING
                                   N00 Routing
                                   Info Digit 24 Functionality
NOOR00002                          N00/NXX TCAP SERVICES
                                   TCAP Based N00 Routing
                                   TCAP Based NXX Dialing Plan
                                   Auto Code Gapping
                                   N00 TCAP Route Advance
NSER0001                           NETWORK SERVICES
                                   ANI Delivery on DALTIE
                                   STS/Netinfo Mapping
NSER0003                           INTER/INTRA IMT SUPPORT
                                   Inter/Intra IMT Support
NPRI0001                           NETWORK INTERFACES PRI
                                   PRI D-Channel Backup
                                   Access Transport
UDWS0001                           UCS DWS
                                   DWS FG-D ISUP
                                   DWS IMT ISUP
                                   DWS PRI
CRDS0001                           CARD SERVICES
                                   Calling Card
                                   Enhanced Calling Card
                                   TCN Log Enhancements
                                   MCCS Dedicated
</TABLE>

December 3, 1996
<PAGE>   64
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         VII. DMS-500 STANDARD FEATURES

1.1   DMS-500 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE     DESCRIPTION
----------         -----------     -----------
<S>                                <C>
CRDS0002                           TCAP BASED CARD SERVICES
                                   CI Command TESTSS
                                   TCAP Based TCN
UTRS0001                           ROUTING
                                   Carrier ID Code Routing
</TABLE>


December 3, 1996
<PAGE>   65
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                        VIII. DMS-500 OPTIONAL FEATURES

1.0      DMS-500 INITIAL SYSTEM OPTIONAL FEATURES

1.1      DMS-500 INITIAL SYSTEM INTEREXCHANGE OPTIONAL SOFTWARE PACKAGES

         The following represents the DMS-500 LLT0B005 base and optional
         software packages that are not included in the price of a DMS-500
         Initial System Model A, Model B and Model C, ("Standard Features").
         The following is a list of Software only (not included in the Schedule
         A Initial System(s); this list does not include any/all required
         Equipment to provide feature functionality.

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG     S/W PACKAGE   DESCRIPTION                              LIST PRICE
----------     -----------   -----------                              ----------
<S>                          <C>                                      <C>
CRDS0003                     MCCS, MVP CARD SERVICES                  $ 50,000
                             MCCS, Mechanized Voice Prompts
NSER0002                     TCAP BASED AUTHCODE AND
                             ACCOUNT CODE VALIDATION                  $ 20,000
                             TCAP Based Account Code and
                               Private Speed Validation
                             TCAP Based Authorization Code
                               Validation
CAIN0200                     CARRIER AIN EXTENSION PARAMETERS         $ 50,000
                             Carrier AIN Extension Parms.
CAIN0300                     CARRIER AIN SCP SIMULATOR                $ 30,000
                             Carrier AIN SCP Simulator
CAIN0400                     CARRIER AIN TEST QUERY                   $ 30,000
                             Carrier AIN Test Query
CAIN0500                     CARRIER AIN CUSTOMIZED
                             DIALING PLAN TRIGGER                    $ 100,000
                             Carrier AIN Customized Dialing
                               Plan Trigger
CAIN0501                     CARRIER AIN SPECIFIC DIGIT
                             TRIGGER                                 $ 100,000
                             Carrier AIN Specific Digit Trigger
</TABLE>

December 3, 1996
<PAGE>   66
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                        VIII. DMS-500 OPTIONAL FEATURES

1.2      DMS-500 INITIAL SYSTEM LOCAL OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>

Feature/
Master Pkg      S/W Package     Description                                             List Price
----------      -----------     -----------                                             ----------
<S>             <C>             <C>                                                     <C>
Automatic Call Distribution
---------------------------
ACD00001                        Meridian ACD Base                                       $      0
                ACD00001-V1     ACD Base per Line Fee                                   $    500
                ACD00001-V2     ACD Base per ACD Group Fee                              $  5,000
ACD00005                        ACD Management Information Sys                          $      0
                ACD00005-V1     ACD MIS per ACD Line Fee                                $    250
ACD00006                        ACD Enhanced                                            $ 52,000
ACD00004                        ACD Networking first 100 Lines                          $105,000
                ACD00004-V1     ACD Ntwking Per ACD Line Fee after 
                                first 100 lines                                         $  1,300
ACD00009                        ACD Networking on CCS7                                  $      0
                ACD00009-V1     ACD Ntwking on CCS7 per ACD Line                        $    400
ACD00010                        ACD Networking on PRI                                   $      0
                ACD00010-V1     ACD Ntwking on PRI per ACD Line                         $    400
ACD00002                        CompuCALL Base                                          $      0
                ACD00002-V1     CompuCALL per SVC Fee                                   $  7,500
ACD00007                        CompuCALL for ACD                                       $      0
                ACD00007-V1     CompuCALL for ACD per SVC fee                           $ 42,000
ACD00008                        Centrex Coordinated Voice and Data                      $      0
                ACD00008-V1     Centrex CVD per CTX Line Fee                            $  5,000

Advanced Intelligent Networking (AIN)
------------------------------------
AIN00002                        AIN Essentials Release 0.1                              $700,000
AIN00001                        AIN Primer                                              $      0
                AIN00001-A1 A   IN Primer Annual Fee                                    $ 80,000

Datapath
--------
DTP00001                        Datapath                                                $ 17,500
DTP00002                        CLASS on Datapath 1st 100 Datapath Lines                $  4,000
                DTP00002-V1     CLASS on DTP each addtl. 100 Lines                      $  1,000
DTP00003                        Data Call Tester                                        $      0

</TABLE>


December 3, 1996
<PAGE>   67
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                        VIII. DMS-500 OPTIONAL FEATURES

1.2      DMS-500 INITIAL SYSTEM OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG         S/W PACKAGE   DESCRIPTION                         LIST PRICE
----------         -----------   -----------                         ----------
<S>                              <C>                                   <C>
DIALABLE WIDEBAND-SERVICES
--------------------------
NIO00004                         NIO DIALABLE WIDEBAND SVC BASE        $ 50,000
                   NIO00004-Vl   NIO DWS per Access Loop Fee           $ 11,500
NIO00023                         NI0 INTERTOL ISUP & SS7               $200,000
NIO00027                         NIO DWS FLEXIBLE ACC                  $ 71,500
NIO00028                         NIO DWS CARRIER ACC                   $200,000

EMERGENCY NUMBER-SERVICES
-------------------------
ENS00002                         ENS ACD PSAP                          $ 47,000
                   ENS00002-VI   ENS ACD per Agent Fee                 $  2,000
ENS00003                         ENS STANDARD SELECTIVE ROUTINGDB      $145,000

EQUAL ACCESS
------------
EQA00003                         EQA CELULAR INTRCNECT-EO              $ 15,000
EQA00004                         EQA CELLULAR INTERCONNECT-TANDEM      $ 25,000
EQA00007                         EQA EA ALT SW POINT                   $ 35,000
EQA00010                         EQA ENWATS OPRATN(POTS)               $ 20,000
EQA00011                         EQA EQUAL ACCESS OSS                  $  8,000
EQA00005                         EQA INTERMEDIATE TANDEM               $ 20,000
EQA00012                         EQA C7ISUP INTERLATA CONN AT          $120,000

LATA EGUAL ACCESS SYSTEM
------------------------
LEA00001                         LEAS TOLL 1ST 50K DIRECTORY NO        $145,000
                   LEA00001-V1   LEAS Toll each addtl 10K DN's         $ 20,000
LEA00002                         LEAS LOCAL                            $ 22,500

MERIDIAN DIGITAL CENTREX
------------------------
MDC00034                         MDC PRO ENHANCED WATS                 $ 20,000
MDC00018                         MDC PRO MDR VIA AMA STREAM            $ 20,000
MDC00002                         MDC MERIDIAN SPECIAL ATTENDANT
                                 CONSOLE                               $ 21,733
MDC00012                         MDC TAILORED MDC 1                    $ 26,500
NMC00013                         MDC TAILORED MDC 2                    $ 40,000
MDC00016                         MDC TAILORED NTWK ADDRESS
                                 REGISTERS                             $ 50,000
MDC00035                         MDC TEEN SERVICE                      $      0
                   MDC00035-VI   MDC Teen Svc per 100 Line Fee         $  5,000
MDC00033                         MDC NAME/NUMBER
                                 BLOCKING                              $ 15,000
NMC00005                         MDC MBG MINIMUM                       $ 73,500
MDC00006                         MDC MBG STANDARD                      $175,000
MDC00011                         MDC PRIVATE VIRTUAL NTWKING           $195,000
MDC00036                         MDC SMDR FOR PVN                      $ 15,000
</TABLE>


December 3, 1996
<PAGE>   68
                                                       MIDCOM Product Attachment
                                   SCHEDULE A
                        VIII. DMS-500 OPTIONAL FEATURES

1.2      DMS-500 INITIAL SYSTEM OPTIONAL SOFTWARE PACKAGES (CONT.)


<TABLE>
<CAPTION>

Feature/
Master Pkg              S/W Package             Description                     List Price
----------              -----------             -----------                     ----------
<S>                     <C>                     <C>                             <C>

National ISDN NI0-NI1

NIO00007                                        NIO ISDN BASE (Reqd all ISDN)   $ 68,500
                        NIO00007-VI             ISDN Base Per 100 ISDN Lines    $    500
                        NIO00007-V2             ISDN Base per 1B+D Line fee     $    100
                        NIO00007-V3             ISDN Base per 2B+D Line Fee     $    250
NIO00008                                        NIO NI-1 BRI                    $251,000
                        NIO00008-VI             NI0 NI-1 BRI per LCMI fee       $  7,200
NIO00009                NIO NI-1 BRI            Enh. Maintenance                $ 68,000
NIO00022                                        NIO ISDN PRI Base               $ 30,000
                        NIO000022-VI            NIO ISDN PRI Base per PRI
                                                link fee                        $  2,000
NIO00011                                        NIO NI-1 PRI                    $ 66,500
                        NIO00011-VI             NIO NI-1 PRI per link fee       $  4,800
NIO00012                                        NIO NI-1 PRI Interworking with
                                                4ESS/5ESS                       $ 50,000
NIO00013                                        NIO NI-1 PRI Networking         $ 28,000
                        NIO00013-VI             NIO NI-1 PRI Ntwking per link   $  3,750
                                                DataSPAN                        $      0
NIO00002                NIO00002-VI             DataSPAN per LPP fee            $ 20,000
NIO00010                                        NIO NI-1 Packet Services        $ 75,000

Remote services

BAS00012                                        BAS Remote                      $ 22,500
                        BAS00012-V1             BAS Remote per Remote Fee       $  5,500
                        BAS00012-V2             BAS Remote per LCM Fee          $    700
BAS00009                                        BASE RSC-S Sync                 $ 30,000
                        BAS00009-V1             BAS Remote per RSCS Fee         $120,000

Residential enhanced services

RES00001                                        RES Access Management           $  8,000
RES00002                                        RES Adv. Custom Calling Feat.   $ 12,500
                        RES00002-V1             RES ACCF per 100 lines          $  2,500
RES00011                                        RES Unvsl Access to CLASS
                                                First 5K Equipped Lines         $115,500
RES00013                                        RES Ext. Bridged Services       $  7,500
RES00014                                        RES Call Wake-up Service        $  5,000
                        RES00014-V1             RES CWUS per 100 RES Lines      $  2,000
RES00015                                        RES Sub. Activated Call         $ 20,000
                                                Blocking
RES00016                                        RES Expansion Services          $ 20,000
RES00018                                        RES & MDC Warm Line             $  5,000
RES00003                                        RES Display Funct. & Privacy    $ 30,000
                        RES00003-V1             Per 100 CLASS Lines Fee         $  1,500


</TABLE>




December 3, 1996
<PAGE>   69
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                        VIII. DMS-500 OPTIONAL FEATURES

1.2     DMS-500 INITIAL SYSTEM OPTIONAL SOFTWARE PACKAGES (CONT.)


<TABLE>
<CAPTION>
FEATURE/
MASTER PKG.                     S/W PACKAGE             DESCRIPTION                     LIST PRICE
-----------                     -----------             -----------                     ----------
Residential Enhanced Services Cont.
-----------------------------------
<S>                             <C>                     <C>                             <C>
RES00021                                                RES ANONYMOUS CALLER REJ.       $30,000
                                RES00021-V1             Per 100 CLASS Lines Fee         $ 3,000
RES00022                                                RES CALLING NAME DELIVERY BLK   $ 8,000
RES00023                                                RES CALLING NAME DISPLAY SW.    $20,000
RES00024                                                RES VSLE & CALL LOGGING         $50,000
RES00025                                                RES CALL WAITING DISPLAY        $     0 
                                RES00025-V1             Per 5K equipped switch lines    $15,000
RES00026                                                RES ENH. CALL WAITING DISPLAY   $     0
                                RES00026-V1             Per 5K equipped switch lines    $10,000
RES00027                                                RES VISUAL MSG. WAITING         $10,000
RES00004                                                RES INTERFACE FUNCTIONALITY     $75,000
                                RES00004-V1             RES I/F Funct. per 25 LINKS     $10,000
RES00028                                                RES BULK CALL LINE ID FIRST
                                                        50 LINKS                        $20,000
                                RES00028-V1             RES BCL ID each addtl 25 link   $10,000
RES00039                                                RES SMDI CLID SUPPRESSION       $24,000
RES00029                                                RES AUTOMATIC RECALL            $ 5,000
RES00030                                                RES CUSTOMER TRACING            $ 3,500
                                RES00030-V1             RES CT per 100 Class Lines      $ 1,500
RES00031                                                RES CUSTOMER TRACING ENHANCED   $ 3,500
RES00032                                                RES SELECTIVE CALL FORWARD      $10,000
                                RES00032-V1             RES SCF per 100 Class Lines     $ 1,500
RES00033                                                RES SELECTIVE CALL REJECTION    $10,000
RES00034                                                RES DIST. RINGING CALL WAITING  $10,000
                                RES00034-V1             RES DRCW per 100 Class Lines    $ 3,000
RES00035                                                RES SELECTIVE CALL ACCEPTANCE   $     0
                                RES00035-V1             RES SCA per 100 SCA lines       $ 3,000
RES00007                                                RES SIGNALING, ROUTING
                                                        AND OAM                         $20,000
</TABLE>


1.3     DMS-500 SYSTEM OPTIONAL FEATURES -- PRICING

        Refer to Section VII of this Product Attachment for DMS-500 Optional
        Software Pricing Discounts.



December 3, 1996
<PAGE>   70
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                          IX. DMS-250 STANDARD FEATURES

I.     DMS-250 INITIAL SYSTEM STANDARD FEATURES

1.1  DMS-250 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES

The following represents the DMS-250 UCS05 base and optional Software packages
that are included in the price of a DMS-250 Initial System Model D, Model E and
Model F, ("Standard Features").  The following is a list of Software only
included in the Schedule A DMS-250 Initial System(s); this list does not
include any/all required Equipment to provide feature functionality.

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG     S/W PACKAGE     DESCRIPTION
----------     ------------    -----------
<S>            <C>             <C>
UCS00005                       UCS TANDEM SERVICES BASE
--------                       ------------------------
               NTX292BA        Enhanced Security-without Password Encryption 
               NTX702BB        DMS-500 Universal Master Package (UCS)        
               NTX000AA        Bilge                                         
               NTX001AA        Common Basic                                  
               NTX048AA        Synchronization                               
               NTX051AA        Automatic Trunk Testing                       
               NTX053AA        Maintenance Assistance Package                
               NTX055AA        Trunk Test Position (TTP)                     
               NTX055AB        TTP Digit Verification                        
               NTX055AC        TTP Transmission Measurement                  
               NTX056AA        Enhanced Administration                       
               NTX060AB        Network Management                            
               NTX060BB        Network Management - Enhanced                 
               NTX072AA        International Direct Distance Dialing (IDDD)  
               NTX074AA        Disk Data Storage Storage System              
               NTX085AA        Traffic Separation Peg Count                  
               NTX087AA        Traffic Separation Usage                      
               NTX088AA        Traffic Separation Report                     
               NTX099AA        Operational Measurements Enhancements         
               NTX122AA        OM Call Attempts Summary                      
               NTX136AA        Automatic Transmission Measuring System       
               NTX202AA        DMS-250 Operational Measurements on Tape      
               NTX203AA        DMS-250 104 Testlines                         
               NTX220BA        DMS-250 Base Package (Type II)                
               NTX221BA        DMS-250 Call Detail Recording (Type II) Billing
               NTX222BA        DMS-250 Call Processing (Type II)             
               NTX227BA        DMS-250 Time Of Day Routing                   
               NTX228BA        DMS-250 DCM Channel Unit Cross Reference      
               NTX230BA        DMS-250 Speed Numbers (Public/Private)        
               NTX231BA        DMS-250 Incoming Exclusion                    
               NTX234BA        DMS-250 Authcodes (Type II)                    
               NTX235BA        DMS-750 Restricted Usage By Date and Time     
               NTX236BA        DMS-250 Alternate Trunk Group Treatments      
               NTX239BA        DMS-250 Translation Verification              
               NTX244AB        Enhanced Sequential Trunk Hunting             
               NTX269AA        Universal Tone Receivers                      
               NTX270AA        New Peripheral Maintenance Package            
               NTX291AA        Enhanced Real Time Indicator                  
               NTX321BA        DNIS-250 Generic Offnet Access Trunks (FG-B)  
</TABLE>


December 3, 1996
<PAGE>   71
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         IX. DMS-250 STANDARD FEATURES

1.1      DMS-250 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG     S/W PACKAGE     DESCRIPTION
----------     ------------    -----------
<S>            <C>             <C>
UCS00005                       UCS TANDEM SERVICES BASE
--------                       ------------------------
               NTX702BB        DMS-250 Universal Master Package (UCS)       
               NTX342BA        DMS-250 Equal Access Base Package (FG-D)     
               NTX343BA        DMS-250 Equal Access (Type II) - ANI Scrn
               NTX347AA        DMS Base Data Communication Software          
               NTX351BA        DMS-250 Automatic Trunk Routining               
               NTX445AB        Operational Measurement Selective Output      
               NTX738AC        Switch Performance Monitoring System (SPMS)   
               NTX801AA        Toll Features I                               
               NTX827AA        New Peripherals Performance Measurements      
               NTX903AA        Transmission Measurements                     
               NTXA11AA        Patch Administration & Downloading via X.25   
               NTXG22AA        DMS-250 UCS Outgoing FG-D Enhancements        
               NTXG24AA        DMS-250 Integrated Echo Cancellor             
               NTXJ35AA        Maintenance Managers Report                   
               NTXL02AA        DMS-250 UCS Dialing Plan Enhancements         
               NTXL05AA        DMS-250 Roaming PINs                          
               NTXL79AA        DMS-250 XPM+ for DTC7/DTCI                    
               NTXR34AB        XPM Plus Basic                                
               NTXR42AA        Firmware Downloading                          
               NTXG18AA        DMS-250 Safe Store TAP (X.25 Applications)     
               NTXM70AA        UCS Tandem Services Base                      
               NTX065AA        Service Analysis                              
               NTX142AA        DS-1 64 KBPS Clear                           
               NTX143AA        DS-1 ESF                                      
               NTX167AB        CCS7 Trunk Signalling                         
               NTX226BA        DMS-250 ATB by NPA Using Operational Meas.    
               NTX232BA        DMS-250 ATB by NPA Using Logs                
               NTX233BA        DMS-250 Off Hook Queuing                      
               NTX237AA        DMS-250 Nailed Up Connections                 
               NTX340BA        DMS-250 Adaptive Routing                      
               NTX346BA        DMS-250 Intra Lata Intra State Screening      
               NTX361BA        DMS-250 CCS7 IMTS                            
               NTX368BA        DMS-250 Multiple Authcode Sets                
               NTX437AA        Random Conditional Routing                    
               NTX550AA        CCS7 Transaction Service Support              
               NTX836AA        LPP V.35 Subrate Links                        
               NTX839AB        LPP Enhanced Maintenance and Bert             
               NTX840AA        LIU7 Gateway Message Screening                
               NTX882AA        Bit Error Ratio Indicator for Toll Switches   
               NTX883AA        Inter Office Trunk Bit Error Rate             
               NTX885AB        Switch Pat Diagnostics                        
               NTX945AA        MS Base Link Maintenance                      
               NTXA67AA        Extended XPM Diagnostics                      
               NTXE01AA        Enhanced Network Basic (ENET)                 
</TABLE>


December 3, 1996
<PAGE>   72
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         IX. DMS-250 STANDARD FEATURES

1.1    DMS-250 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG     S/W PACKAGE     DESCRIPTION
----------     ------------    -----------
<S>            <C>             <C>
UCS00005                       UCS TANDEM SERVICES BASE
--------                       ------------------------
               NTXM70AA        UCS Tandem Services Base Cont.
               NTXE32AA        CCS7 Preventative Cyclical Retransmission
               NTXE65AA        MPC X25 Interface
               NTXE98AA        High Speed MPC
               NTXF05AA        Ethernet Interface Unit
               NTXF19AA        TCP/IP Protocols
               NTXF20AA        LMS on LPP
               NTXF71AB        SuperNode Enhanced Messaging
               NTXG10AA        DMS-500 CNS CCITT 1984 X.25 Datacom
               NTXG13AA        DMS BASE Data Access Interface Session
               NTXG18BA        DMS-250 Safe Store Tap
               NTXG20AA        DMS-250 SS7 FG-D
               NTXG28AA        DMS-250 Enhanced COS Screening
               NTXG34AA        DMS-250 Trunk Group and CLLI name analysis
               NTXG35AA        DMS-250 Paystation Pretranslator
               NTXG42AA        DMS-250 SS7 IMT Terminations to DTU
               NTXG46AA        DMS-250 Direct Termination Service
               NTXG49AA        DMS-250 UCS SS7 UCP (Base ISUP)
               NTXJ40AA        LIU7 Gateway Verification Tools
               NTXJ41AA        CCS7 Test Tools
               NTXJ44AA        SLM File System
               NTXJ94AA        Mandatory Parallel AMA
               NTXL01AB        DMS-250 UCS Account Code Screening Enh.
               NTXL03AA        DMS-250 UCS to USP ISUP Interworking
               NTXL04AA        DMS-250 UCS SS7 Intra/Inter Networking
               NTXL08AA        DMS-250 UCS X.25 Transport
               NTXL09AA        DMS-250 UCS PRA
               NTXL11AA        DMS-250 UCS to MCI ISUP Interworking
               NTXL12AA        DMS-250 UCS to FGD ISUP Interworking
               NTXL14AA        DMS-250 UCS International Partitioning
               NTXL47AA        DMS-250 Lower Layer Compatibility
               NTXN16AA        Enhanced Dram
               NTXN18AA        FBUS LIU Base
               NTXN19AA        LIU7 for LPP Based CCS7 Applications
               NTXN68AA        XPM Broadcast Patching
               NTXN83AA        LIS Common
               NTXP10AA        Network Module Software
               NTXP13AA        Enet Switch Path Diagnostics
               NTXP14AA        Dirp Parallel Storage Size Increase
               NTXQ51AA        MS SR512 Lis Controller
               NTXR70AA        CM Base for OPC
               NTXR72AA        CCS7 MTP/SCCP for LPP
               NTXS11AA        File Transfer Protocol
                               
</TABLE>

December 3, 1996

<PAGE>   73
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                         IX. DMS-250 STANDARD FEATURES

1.1     DMS-250 INITIAL SYSTEM BASE AND OPTIONAL SOFTWARE PACKAGES (CONT.)

<TABLE>
<CAPTION>
FEATURE/
MASTER PACKAGE     S/W PACKAGE     DESCRIPTION
--------------     -----------     -----------
<S>                <C>             <C>
UCS00005                           UCS TANDEM SERVICES BASE
                   NTXM70AA        UCS TANDEM SERVICES BASE CONT.
                   NTXX26AA        DMS-250 UCS X.25 Data Transport
                                   Enhancements
                   NTXX30AA        UCS Enhanced Dialing Plan Phase II
                   NTXX32AA        Enhanced PANI on UCS
                   NTXX42AA        Disallow Reorigination on EANT FG-D
                                   Trunks
CRDS0001                           CARD SERVICES
                                   Calling Card
                                   Enhanced Calling Card
                                   TCN Log Enhancements
                                   MCCS Dedicated
CRDS0002                           TCAP BASED CARD SERVICES
                                   CI Command TESTSS
                                   TCAP Based TCN
N00R00001                          N00 ROUTING
                                   N00 Routing
                                   Info Digit 24 Functionality
N00R00002                          N00/NXX TCAP SERVICES
                                   TCAP Based N00 Routing
                                   TCAP Based NXX Dialing Plan
                                   Auto Code Gapping
                                   N00 TCAP Route Advance
NSER0001                           NETWORK SERVICES
                                   ANI Delivery on DALTIE
                                   STS/Netinfo Mapping
NSER0003                           INTER/INTRA IMT Support
                                   Inter/Intra IMT Support
NPRI0001                           NETWORK INTERFACES PRI
                                   PRI D-Channel Backup
                                   Access Transport
UDWS0001                           UCS DWS
                                   DWS FG-D ISUP
                                   DWS IMT ISUP
                                   DWS PRI
UTRS0001                           ROUTING
                                   Carrier ID Code Routing
</TABLE>

December 3, 1996

<PAGE>   74
                                                       MIDCOM Product Attachment

                                   SCHEDULE A
                          X. DMS-250 OPTIONAL FEATURES

1.0     DMS-250 INITIAL SYSTEM OPTIONAL FEATURES - INTEREXCHANGE

The following represents the DMS-250 UCS05 optional InterExchange Features
("DMS-250 Optional Feature - InterExchange") that are not included in the
DMS-250 Initial System Models D, E or F. Such DMS-250 Optional Feature -
InterExchange may be ordered by Buyer for the DMS-250 Initial System Models D,
E and F or with a Software Upgrade at the fees specified below.

<TABLE>
<CAPTION>
FEATURE/
MASTER PKG     S/W PACKAGE     DESCRIPTION                          LIST PRICE
----------     -----------     -----------                          ----------
<S>                            <C>                                   <C>
CRDS0003                       MCCS MVP CARD SERVICES                 $ 50,000
                               MCCS Mechanized Voice Prompts
NSER0002                       TCAP BASED AUTHCODE AND
                               ACCOUNT CODE VALIDATION                $ 20,000
                               TCAP Based Account Code and
                                 Private Speed Validation
                               TCAP Based Authorization Code
                                 Validation
CAIN0200                       CARRIER AIN EXTENSION PARAMETERS       $ 50,000
                               Carrier AIN Extension Parms.
CAIN0300                       CARRIER AIN SCP SIMULATOR              $ 30,000
                               Carrier AIN SCP Simulator
CAIN0400                       CARRIER AIN TEST QUERY                 $ 30,000
                               Carrier AIN Test Query
CAIN0500                       CARRIER AIN CUSTOMIZED
                               DIALING PLAN TRIGGER                  $ 100,000
                               Carrier AIN Customized Dialing
                                 Plan Trigger
CAIN0501                       CARRIER AIN SPECIFIC DIGIT
                               TRIGGER                               $ 100,000
                               Carrier AIN Specific Digit Trigger
</TABLE>

1.1      DMS-250 SYSTEM OPTIONAL FEATURES - INTEREXCHANGE PRICING

         Refer to Section V of this Product Attachment for DMS-250 Optional
         Software Pricing Discounts.


December 3, 1996
<PAGE>   75
                                                              Product Attachment
                                                                         Page 13

                                   SCHEDULE B
                              SERVICES AND CHARGES

ENGINEERING

1.     Nortel shall engineer each System furnished hereunder in accordance with
       Nortel's engineering practices applicable to such Initial System at the
       time such engineering is performed.

2.     Nortel's charges for engineering each Initial System are included in the
       prices and fees for the Initial System set forth in Schedule A.

3.     The provision of any other engineering by Nortel and the charges
       associated therewith shall be as subsequently agreed in writing by
       Nortel and Buyer.

INSTALLATION

1.     Nortel shall install each Initial System furnished hereunder at the
       applicable Installation Site in accordance with Nortel's installation
       practices applicable to such Initial System at the time such
       installation is performed.

2.     Nortel's charges for performance of such installation are included in
       the prices and fees for the Initial System set forth in Schedule A.

3.     The provision of any other installation by Nortel and the charges
       associated therewith shall be as subsequently agreed in writing by
       Nortel and Buyer.

TRAINING

1.     As applicable, with each Initial System or DMS-250 to DMS-500 Upgrade
       furnished hereunder, Nortel shall provide to Buyer at no additional
       charge the following number of training days at Nortel's Training Center
       currently located in Raleigh, North Carolina:

                 Initial System Model A through C, one hundred (100) days.
                 Initial System Model D through F, fifty (50) days.
                 DMS-250 to DMS-500 Upgrade, fifty (50) days.

       (Note: Initial System models are defined in Schedule A, Section II, as
       appropriate.)

       Such training shall be in any of the courses scheduled to be provided at
       that Training Center as set forth in NTI's applicable Technical Training
       Course catalog with respect to the Products described in Schedule A to
       this Attachment.
<PAGE>   76
                                                              Product Attachment
                                                                         Page 14

2.       Buyer shall be responsible for the payment of all travel and living
         expenses of its employees whom Buyer sends to receive such training.

3.       Additional Training in such courses shall be provided by Nortel to
         Buyer subject to availability and scheduling of such courses.  NTI may
         change the schedule of such courses at any time.  Such additional
         training shall be provided at NTI's then-current charges.

4.       All training provided by NTI shall consist of such materials and cover
         such subject as NTI in its sole discretion determines to be
         appropriate.  Nortel makes no representation concerning the ability of
         anyone to satisfactorily complete any training.

5.       Nortel may add to, or delete from, the subject matter and or medium of
         any of the training courses which NTI provides.  In addition, NTI may
         reschedule such courses as NTI determines to be appropriate.

6.       The availability of any training to Buyer as set forth above shall be
         subject to any prerequisites identified by NTI in its training catalog
         or other documentation with respect to such training.

ADDITIONAL SERVICES

1.       All other services to be furnished hereunder shall be subject to
         written agreement of the parties which shall set forth the terms and
         conditions applicable to the provision of such services and a
         description of such services and the charges for such services.
<PAGE>   77
                                                              Product Attachment
                                                                         Page 15
                                   SCHEDULE C
                                    DELIVERY

The delivery schedule shall be mutually agreed to by the parties and set forth
in any Order for Products.
<PAGE>   78
                                                              Product Attachment
                                                                         Page 16

                                   SCHEDULE D
                                 DOCUMENTATION

Certain documentation with respect to the Products may be made available to
Buyer on CD-ROM pursuant to the terms and conditions set forth below.

In addition, Nortel may furnish to Buyer such other documentation with respect
to the Products as Nortel deems appropriate.

HELMSMAN TERMS AND CONDITIONS

1.  DEFINITIONS

"CD-ROM" shall mean a compact disk with read-only memory.

"CD-ROM Software" shall mean the computer programs which provide basic logic,
operating instructions or user-related application instructions with respect to
the retrieval of CD-ROM Documentation, along with the documentation used to
describe, maintain and use such computer programs.

"CD-ROM Documentation" shall mean the documentation that Nortel makes available
to its customers on CD-ROM with respect to DMS-250, DMS-300, and/or DMS-STP
Systems.

2.  SCOPE

With the delivery of each Initial System ordered by Buyer, Nortel shall deliver
a CD-ROM on which the appropriate CD-ROM Documentation is contained and a user
manual which shall set forth the procedures by which Buyer may use the CD-ROM
Software to access to the CD-ROM Documentation.

Buyer shall be solely responsible for obtaining, at its cost and expense, any
computer or other equipment and software required to use the CD-ROM, CD-ROM
Software and/or CD-ROM Documentation.

Buyer may order additional CD-ROMs from Nortel at Nortel's then current fees
therefor, and any such additional CD-ROMs shall be subject to these terms and
conditions.

3.  LICENSE

Upon delivery of the CD-ROM, Nortel shall grant to Buyer a non-exclusive,
non-transferable and non-assignable license, subject to these terms and
conditions: