<PAGE>

                                                                  Exhibit 10.52


                       INTELLIVOICE COMMUNICATIONS, INC.

                           1995 INCENTIVE STOCK PLAN
                           -------------------------

                                JANUARY 24, 1995

                         (as amended October 10, 1995)



1.   Establishment and Purpose of the Plan

     The purpose of this Plan is to provide a flexible means of compensation and
     motivation for outstanding performance by employees of the Company,
     directors of the Company, and other certain persons to further the
     continued growth and profitability of the Company.

2.   Definitions

     (a)  Board of Directors.  The Board of Directors of the Company.
          ------------------

     (b)  Common Stock.  The common stock of the Company, $.01 par value.
          ------------

     (c)  Company.  Intellivoice Communications, Inc., a Delaware corporation,
          -------
          and any successor or transferee of substantially all of its business
          or assets.

     (d)  Disinterested Person.  The Compensation Committee of the Board of
          --------------------
          Directors, which committee shall have at least three members, each of
          whom shall be a Disinterested Person.

     (e)  Person.  A "disinterested person" as defined in Rule 16b-3.
          ------

     (f)  Employee.  A full-time key employee of the Company, including an
          --------
          officer who is such an employee.

     (g)  Fair Market Value.  As applied to a specific date, the fair market
          -----------------
          value of the share of Common Stock as of such date as determined by
          the Committee for purposes of an Incentive Stock Option in accordance
          with the then current regulations of the U.S. Secretary of the
          Treasury.

     (h)  Incentive Stock Option.  Any Option intended to meet the requirements
          ----------------------
          of an incentive stock option as defined in Section 422.

     (i)  Non-Qualified Stock Option.  Any Option not intended to be an
          --------------------------
          Incentive Stock Option.
<PAGE>

     (j)  Option.  An option to purchase Common Stock granted under the Plan,
          ------
          including both an Incentive Stock Option and a Non-Qualified Stock
          Option.

     (k)  Person.  An individual, a partnership, a corporation, or any other
          ------
          private, governmental or other entity.

     (l)  Plan.  The Intellivoice Communications, Inc. 1995 Incentive Stock Plan
          ----
          herein set forth, as the same may from time to time be amended.

     (m)  Rule 16b-3.  Rule 16b-3 under the Securities Exchange Act of 1934, as
          ----------
          amended, and any successor rule or regulation.

     (n)  Section 422.  Section 422 of the Internal Revenue Code of 1986, as
          -----------
          amended, or any successor statute.

3.   Eligibility

     A grant under this Plan may be made to any Employee, any director of the
     Company, or any other person as to whom the Committee determines that
     making such grant is in the best interests of the Company; provided,
     however, that (i) no grant may be made to a director of the Company who
     serves on the Committee other than as provided under Rule 16b-3, and (ii)
     no, grant of an Incentive Stock Option may be made to a person other than
     an Employee.

4.   Plan Administration

     This Plan shall be administered by the Committee.  The Committee shall have
     full power to interpret and administer this Plan and full authority to act
     in selecting the grantees and in determining type and amount of grants, the
     terms and conditions of grants, and the terms of agreements which will be
     entered into with grantees governing such grants.  The Committee shall have
     the power to make rules and guidelines for carrying out the Plan and to
     make changes, in such rules and guidelines from time to time as it deems
     proper.  Any interpretation by the Committee of the terms and provisions of
     the Plan and the administration thereof and all action taken by the
     Committee shall be final and binding.

5.   Shares Subject to the Plan

     Subject to adjustment as provided in Section 9, the total amount of shares
     of Common Stock available for grant under this Plan shall be up to 159,990
     shares of Common Stock of the Company.  Shares of Common Stock issued
     hereunder may consist, in whole or in part, of authorized and unissued
     shares, treasury shares and shares acquired in the open market or by
     private purchase by the Company.  Any
<PAGE>

     Common Stock which is purchased shall be purchased by the Company at prices
     no higher than the Fair Market Value of such Common Stock at the time of
     purchase. If for any reason any shares of Common Stock issued under any
     grant hereunder are forfeited or cancelled, or a grant otherwise terminates
     or is terminated for any reason without the issuance of any shares, then
     all such shares, to the extent of any such forfeiture, cancellation or
     termination, shall again be available for grant under this Plan.

6.   Types of Grants

     (a)  The Committee may make such grants under this Plan of Incentive Stock
          options and Non-Qualified Stock Options as in its discretion it deems
          advisable to effect the purpose of the Plan.  Such grants may be
          issued separately or in combination, and additional grants may be
          issued in combination with grants previously issued under this Plan or
          otherwise.

     (b)  The exercise price of an Option or other grant shall equal at least
          100% of the Fair Market Value of the shares of Common Stock on the
          date of such grant and be paid in cash or such other consideration as
          the Committee may determine consistent with applicable law, which may
          include without limitation (i) shares of Common Stock; and (ii) the
          withholding, from the shares of Common Stock receivable on exercise,
          of shares of Common Stock with a Fair Market Value as of the date of
          exercise equal to the exercise price.

7.   Options

     (a)  Each Option shall have such terms and conditions as the Committee
          shall determine, except that no Option shall have a term of more than
          ten years.  A grantee shall have no rights of a shareholder with
          respect to any Shares of Common Stock subject to an Option unless and
          until a certificate for such shares shall have been issued.

     (b)  All the provisions of Section 422 and the regulations thereunder as in
          effect from time to time are hereby incorporated by reference herein
          with respect to Incentive Stock Options to the extent that their
          inclusion in this Plan is necessary from time to time to preserve
          their status as incentive stock options for purposes of Section 422.
          Each provision of the Plan and each agreement relating to an Incentive
          Stock Option shall be construed so that it shall be an incentive stock
          option for purposes of Section 422, and any provisions thereof which
          cannot be so construed shall be disregarded.
<PAGE>

8.   Adjustments Upon Changes in Capitalization

     In the event of a reorganization, recapitalization, stock split, stock
     dividend, issuance of securities convertible into Common Stock, combination
     of shares, merger, consolidation or any other change in the corporate
     Structure of the Company affecting Common Stock, or a sale by the Company
     of all or substantially all of its assets, or any distribution to
     shareholders other than a normal cash dividend, or any assumption or
     conversion of outstanding grants as a result of an acquisition, the Board
     of Directors shall make appropriate adjustment in the number and kind of
     shares authorized by the Plan and any adjustments in outstanding grants as
     it deems appropriate.

9.   Termination and Amendment

     (a)  This Plan shall become effective upon its approval by the shareholders
          of the Company.  It shall remain in full force and effect unless
          terminated by the Board of Directors, which shall have the power to
          amend, suspend, terminate or reinstate this Plan at any time, provided
          that no amendment which increases the number of shares of Common Stock
          subject to the Plan, or materially adversely affects the availability
          of Rule 16b-3 with respect to this Plan, shall be made without
          shareholder approval.

     (b)  Without limiting the generality of the foregoing, the in Board of
          Directors may (i) amend any limitations in this Plan if and when they
          are no longer required under Rule 16b-3 or Section 422 and (ii) amend
          the provisions of this Plan to assure its continued compliance with
          Rule 16b-3 and Section 422.

10.  Non-Assignability

     Grants are not transferable other than by will or the laws of descent and
     distribution.  A grant is exercisable during the grantee's lifetime only by
     the grantee or his or her guardian or legal representative.

11.  Exercise by Estate

     Any provision of this Plan to the contrary notwithstanding, unless
     otherwise determined by the Committee, the estate of any grantee shall have
     one year from the date of such grantee's death to exercise any grant
     hereunder, or such longer period as the Committee may determine, except
     that this sentence shall in no event extend the term of any Incentive Stock
     Option beyond ten years.
<PAGE>

12.  General Provisions

     (a)  Nothing contained in this Plan, or in any grant made pursuant to the
          Plan, shall confer upon any grantee any right with respect to terms,
          conditions or continuance of employment by the Company.

     (b)  Appropriate provision may be made by the Committee for all taxes
          required to be withheld in connection with any grant, the exercise
          thereof, and the transfer of shares of Common Stock, in respect of any
          federal, state, local or foreign withholding taxes.  In the case of
          payment in the form of Common Stock, the Company shall have the right
          to retain the number of shares of Common Stock whose Fair Market Value
          equals the amount to be withheld.

     (c)  If any day on or before which such action by the Plan must be taken
          falls on a Saturday, Sunday or legal holiday, such action may be taken
          an the next succeeding day which.  is not a Saturday, Sunday or legal
          holiday.

     (d)  This Plan and all determinations made and actions taken pursuant
          thereto shall be governed by the laws of the State of Delaware without
          regard to principles of conflicts of laws.

     (e)  The Committee may amend any outstanding grants to the extent it deems
          appropriate, provided that, the grantee's consent shall be required in
          the case of amendments adverse to the grantee.