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                                                                    EXHIBIT 10.6

                       FIRST AMENDMENT TO LEASE AGREEMENT

        This First Amendment to Lease Agreement ("First Amendment") is made as
of this 8 day of August 1994 by and between Teachers Realty Corporation
("Landlord") and Voicetek Corporation ("Tenant").

        WHEREAS, Landlord and Tenant have heretofore executed a certain Lease
Agreement dated May 25,1993 ("Lease") pursuant to which Tenant has leased 19,881
rentable square feet of area (the "Original Premises") in a building (the
"Building") known as 19 Alpha Road, Chelmsford, MA; and

        WHEREAS, Landlord and Tenant have agreed that Tenant shall be permitted
to expand the Original Premises and to lease an additional 13,619 rentable
square feet of area in the Building, as more particularly shown on Exhibit A to
this First Amendment (the "New Premises") subject to the terms, covenants and
provisions of the Lease as amended hereby; and

        WHEREAS, the three (3) year Initial Term of the Lease is scheduled to
expire on May 31,1996; and

        WHEREAS, Landlord and Tenant are now desirous of extending the Term of
the Lease a period of five (5) years beginning on the New Premises Commencement
Date (as hereafter defined); and

         WHEREAS, Landlord and Tenant have agreed to enter into this First
Amendment to memorialize their agreements and to otherwise modify and amend the
Lease to (i) reflect the increase in the size of the Premises demised under the
Lease as a result of the addition of the New Premises (ii) to extend the Term of
the Lease for the period of five (5) years beginning on the New Premises
Commencement Date and (iii) to otherwise modify and amend the Lease as
hereinafter set forth.

        NOW, THEREFORE, in consideration of Ten ($10.00) Dollars and other good
and valuable consideration, the receipt and sufficiency of which are
acknowledged, Tenant and Landlord hereby agree as follows:

1.       Changes in Basic Lease Provisions.  Effective as of the New Premises
Commencement Date (as hereinafter defined), the information provided in 
Article I of the Lease captioned "Basic Lease Provisions" will be changed and 
amended in the following respects:

         (a) The definition of the term "Premises Rentable Area" shall be
amended by deleting the reference to "19,881 square feet" and inserting in its
place and stead the number "33,500 square feet".
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         (b) The definition of the term "Basic Rent" shall be amended by
deleting the entire schedule of Basic Rent set forth on the cover page of the
Lease and replacing it with the following:



Period                                                                 Basic Rent                   Monthly Payment
- ------                                                                (per period)                  ---------------
                                                                      ------------                  
                                                                                             
"A. The period beginning on the                                       $89,464.50                   $ 7,455.38 
Commencement Date (as defined in Section                                                                    
4.1 of the Lease) through the date                                                                            
immediately preceding the New Premises                                                                        
Commencement Date (pro-rated on a daily                                                                       
basis for any partial calendar month in                                                                       
which the New Premises Commencement Date                                                                      
shall fall)                                                                                                   
                                                                                                              
B. The approximately two year period                                  $144,050.00                  $12,004.17 
beginning on the New Premises                                                                                 
Commencement Date through and including                                                                       
the last day of the calendar month in                                                                         
which the Second Anniversary of the New                                                                       
Premises Commencement Date shall fall                                                                         
(pro-rated on. a daily basis for any                                                                          
partial calendar month in which the New                                                                       
Premises Commencement Date shall fall)                                                                        
                                                                      $150,750.00                  $12,562.50"
C. The three year period beginning on             
the day immediately following expiration
of the period described in "B" above
through and including the last day of
the Term of this Lease as it is extended
pursuant to paragraph 1(d) of this First
Amendment



        Tenant shall continue to make the monthly payments of the Reimbursement
Rent as defined under Article III, Section 3.1(c) of the Lease and these
payments shall remain unchanged by this First Amendment.

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        (c) The definition of the term "Security Deposit" shall be amended and
increased by deleting the reference to "$22,366.12" and inserting in its place
and stead the number "$32,366.12". Simultaneously with the execution and
delivery of the First Amendment, Tenant shall deposit the additional amount of
$10,000.00 with Landlord to be held (together with the amounts previously
deposited) as security for Tenant's obligations under the Lease pursuant to
Section 14.17 of the Lease. Provided that Tenant is not in default under the
Lease, the Landlord shall apply $10,788.00 (rather than $7,455.37 as stated in
the last sentence of Section 14.17) of the Security Deposit toward the Tenant's
Basic Rent obligation for the last month of the Initial Term.

         (d) The definition of the term "Initial Term" shall be amended and
extended for a period of five (5) years beginning upon the New Premises
Commencement Date; provided, however, that if the New Premises Commencement Date
shall fall on other than the first day of a calendar month, the Initial Term
shall expire on the last day of the calendar month in which the fifth (5th)
anniversary of the New Premises Commencement Date shall fall.

        (e) The definition of the term "Escalation Factor" shall be amended by
deleting "32.57%" and inserting the number "54.88%" in its place and stead.

2. Utilities. The Tenant shall be responsible for the payment of all utilities
servicing the Premises. Notwithstanding anything contained in Section 7.5(c) of
the Lease to the contrary, effective as of the New Premises Commencement Date,
Landlord shall no longer be obligated to pay Landlord's Utility Cost applicable
to gas and electricity used and consumed in the Adjacent Space. Tenant shall be
responsible for all electricity and gas used and consumed in the Premises as
amended as measured in the existing meters

3. Expansion; Generally. Effective as of the New Premises Commencement Date, the
13,619 rentable square feet of area shown on Exhibit A to this First Amendment
shall be added to and included in the Premises demised under the Lease for the
balance of the Term of this Lease and the term "Premises" wherever used in the
Lease shall be deemed to mean and include the New Premises together with the
Original Premises and the terms "Premises Rentable Area" and "Basic Rent" shall
have the meanings ascribed to them in paragraph 1 of this First Amendment.
Accordingly, monthly and annual payments of the Operating Expenses and
Escalation Charges shall be increased to reflect the increase in the size of the
Premises by the addition of the New Premises.

4. Landlord's Expansion Work; New Premises Commencement Date.

4.1 Commencement Date. The provisions of Article IV of the Lease shall not be
applicable to the New Premises and Landlord shall have no obligation whatsoever
to perform the work described in Section 4.2 on page 5 of the Lease. All
construction to be performed by Landlord in the New Premises and the Original
Premises shall be governed by the provisions of this paragraph 4 of this First
Amendment. The New Premises Commencement Date shall be the day following the
date on which the New Premises are "ready for occupancy" as provided in Section
4.2 of this First Amendment Notwithstanding the foregoing, if Tenant's personnel
shall occupy all or any part of the

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New Premises for the conduct of its business prior to the New Premises
Commencement Date, such date shall for all purposes of this Lease be the New
Premises Commencement Date. The Tenant shall, upon demand of the Landlord,
execute a certificate confirming the New Premises Commencement Date as it is
determined in accordance with the provisions of Section 4.2.

4.2 Preparation of the Premises. (a) Landlord shall exercise all reasonable
efforts to complete the work necessary to prepare the New Premises for Tenant's
occupancy and to otherwise alter the Original Premises pursuant to the Plans and
Specifications attached hereto as Exhibit B ("Landlord's Expansion Work"), and
in accordance with Landlord's building standards, but Tenant shall have no claim
against Landlord for failure to complete such Work. Tenant hereby approves all
matters set forth in Exhibit B. The New Premises shall be deemed "ready for
occupancy" on the date upon which Landlord has substantially completed the
Landlord's Expansion Work as certified to Tenant by Landlord by written notice.
To the extent that the requirements of Landlord's Expansion Work, including,
without limitation, the cost of all permits, architectural and engineering fees,
and construction supervision fees, shall exceed a cost of $47,000.00, Tenant
shall pay the cost of such excess requirements (the "OBS Costs") to Landlord as
an additional charge hereunder. Tenant shall pay 1/2 of the OBS Costs prior to
Landlord commencing Landlord's Expansion Work and the other 1/2 of OBS Costs
shall be paid upon completion of Landlord's Expansion Work. Tenant shall, if
requested by Landlord, execute a work letter confirming such excess costs prior
to the time Landlord shall be required to commence work. Failure of Tenant to
timely pay Landlord the amounts required to be paid pursuant to this Section 4.2
shall entitle Landlord to the same rights and remedies as Landlord has against
Tenant for failure to pay Basic Rent when due.

4.3 Conclusiveness of Landlord's Performance. Unless Tenant shall have given
Landlord written notice by the end of the first full calendar month after the
New Premises Commencement Date of specific respects in which Landlord has not
performed Landlord's Expansion Work in compliance with the matters set forth in
Exhibit B, Tenant shall have no claim that Landlord has failed to perform any of
the Landlord's Expansion Work. Except for Landlord's Expansion Work, the
Premises are being leased in their condition, "as is" without warranty or
representation by Landlord. Tenant acknowledges that it has inspected the New
Premises and common areas of the Building and, except for Landlord's Expansion
Work, has found the same to be satisfactory.

5. No Brokers. Tenant warrants and represents that Tenant has dealt with no
broker in connection with the consummation of this Lease and, in the event of
any brokerage claims against Landlord predicated upon prior dealings with
Tenant, Tenant agrees to defend the same and indemnify Landlord against any such
claim.

6. Capitalized terms used herein and not otherwise defined herein shall have the
meanings ascribed to them in the Lease.

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7. Except as herein modified, all terms, covenants and provisions of the Lease
are hereby ratified and affirmed.

WITNESS our hands and seals on the day and year first above written.

                                              LANDLORD:
                                              TEACHERS REALTY CORPORATION

                                              By:     /s/ S. Marc Flannery
                                                 -------------------------
                                                       S. Marc Flannery
                                              Its:     Assistant Secretary
                                                  ------------------------

                                              TENANT:
                                              VOICETEK CORPORATION

                                              By:   /s/ Stephen A. Gorgal
                                                 ------------------------
                                              Its:  Controller
                                                  -----------------------

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                                    EXHIBIT A

                             [VOICETEK FLOOR PLAN]

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                                    EXHIBIT B
                              VOICETEK CORPORATION
                                  19 ALPHA ROAD
                            CHELMSFORD, MASSACHUSETTS

                                 "SCOPE OF WORK"

The following work will be performed by Landlord as specified hereunder and in
accordance with the floor plan dated May 25, 1994 ("Plan").

DEMOLITION

Existing improvements shall be demolished as necessary to accommodate the
proposed layout shown on the Plan. The demolition of the closets adjacent to the
lobby area (as shown on the Plan) has been deleted from the Scope of Work.
Tenant shall be responsible for dismantling and relocating the existing cage
area located at the rear of the Original Premises. All debris shall be removed
from the property and those areas of the Premises affected by construction shall
be cleaned as required during construction and upon completion of construction.

PARTITION

New drywall partitions and soffit will be installed as per the Plan and shall
consist of 2 1/2" metal studs, With 1/2" sheet rock each side, insulated with
fiber glass blanket, taped and ready for finish. All new partitions, unless
otherwise specified on the Plan, will extend to the underside of the existing
ceilings.

Demising wall separating the Premises from the adjoining premises shall be made
to comply with building code requirements.

Minor patching and repairs shall be made to existing walls prior to painting.

CEILING 

Existing suspended acoustic ceiling will be patched and repaired as
required to accommodate the layout and renovations indicated on the Plan. Any
new ceiling tiles or grid shall match existing style.

DOORS

To the extent feasible, existing doors, which are to be eliminated, shall be
relocated to those areas where new doors have been specified on the Plan. A
total of three (3) new doors together with hardware will be furnished of a
quality and finish equivalent to existing doors within the space.
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FLOORING

New carpet will be provided to those areas indicated on the Plan. Allowance will
be $13.50 per square yard installed. Existing flooring, including vinyl
composition tile (V.C.T.), shall be patched as specified on the Plan.

Vinyl base will be installed to those areas which will receive new carpet and as
necessary in those areas where walls are newly constructed or demolished.

WALL FINISHES

All walls and doors to be finished as specified on the Plan. Tenant shall be
responsible for promptly removing all wall hangings in the Original Premises
prior to painting. Additionally Tenant shall disconnect and move any computer
equipment as required to facilitate painting. Tenant shall provide contractor
access to the Premises during non-business hours to complete the painting.

HVAC

New ductwork distribution and diffusers will be furnished and installed as
required in accordance with new layout. Existing diffusers shall be reused to
the greatest extent possible. No special air conditioning (i.e. computer room)
is included in the Scope of Work.

SPRINKLERS

New sprinkler heads Will be provided to satisfy landlord's underwriter and in
accordance with tenant's new layout.

ELECTRICAL

Lighting:

Existing 2'x4' fluorescent light fixtures will be relocated consistent with
Tenant's layout. A total of ten new 2'x4' fluorescent fixtures will be provided
to match existing fixtures. Each newly constructed office shall have a single
pole light switch.
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Power

Thirty standard and five dedicated duplex outlets will be provided to areas of
new construction in locations to be specified by Tenant

Exit signs and emergency lighting will be provided and/or modified as required
by code.


                                        /s/ Stephen A. Gorgal