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                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  FORM 10-K/A
                          Amendment No. 1 to Form 10-K

(Mark One)

[X] ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT
    OF 1934

FOR THE FISCAL YEAR ENDED MARCH 31, 1996

[ ] TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
    ACT OF 1934

For the transition period from _____________ to ______________

                         Commission File Number 0-22210

                                SUMMA FOUR, INC.
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             (Exact name of registrant as specified in its charter)

         Delaware                                      02-0329497
         --------                                      ----------
(State or other jurisdiction of                     (I.R.S. Employer
 incorporation or organization)                  Identification Number)

                               25 SUNDIAL AVENUE
                        MANCHESTER, NEW HAMPSHIRE 03103
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              (Address of principal executive offices) (Zip code)

                                 (603) 625-4050
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              (Registrant's telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act: None

Securities registered pursuant to Section 12(g) of the Act: Common Stock, $.01
par value

Indicate by check mark whether the Registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant

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was required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days.

                              YES: [X]    NO: [ ]

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of Registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to
this Form 10-K. [ ]

The aggregate market value of the voting stock held by non-affiliates of the
Registrant as of April 30, 1996 was $108,484,000. As of May 31, 1996, 6,381,437
shares of the Registrant's Common Stock, $.01 par value, were issued and
outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

(1) Specified portions of the Company's Proxy Statement, which is expected to
    be filed within 120 days after the end of the Company's fiscal year, are
    incorporated by reference into Part III (Items 10, 11, 12 and 13) of this
    Report.

   
This Amendment No. 1 on Form 10-K/A to the Registrant's Annual Report on Form
10-K for the fiscal year ended March 31, 1996 (the "Report") is being filed to
amend and restate the Exhibit Index to the Report. Such Exhibit Index is hereby
amended and restated in its entirety. The actual exhibits previously filed with
the Securities and Exchange Commission with the Report, or incorporated therein
by reference, are not being amended. New exhibits listed are being filed 
herewith.
    
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                                 Exhibit Index

   
Exhibit No.         Description

3.1           -    Amended and Restated Certificate of Incorporation of the 
                   Registrant.(1)

3.2           -    Amended and Restated By-laws of the Registrant.(1)

4.1           -    Specimen Certificate representing the Registrant's Common 
                   Stock.(1)

4.2           -    Rights Agreement, dated February 22, 1995, by and among the
                   Registrant and State Street Bank and Trust Company.(5)

10.1          -    Lease Agreement, dated July 18, 1990, by and between the 
                   Registrant and Northern Manchester Trust.(1)

10.2          -    Lease Agreement, as amended, dated December 21, 1992, by and
                   between the Registrant and 1100 Corporation.(1)

10.3          -    Lease Agreement, dated February 15, 1993 by and between the 
                   Registrant and Atrium Executive Center, Inc.(1)

10.4          -    Registration Agreement, dated July 25, 1984, as amended, by 
                   and among the Registrant and certain investors. (Originally
                   filed as Exhibit 10.5)(1)

10.5          -    Purchase Agreement, dated July 25, 1984, by and among the 
                   Registrant and certain investors. (Originally filed as
                   Exhibit 10.6)(1)

10.6          -    +1994 Executive Incentive Bonus Plan. (Originally filed as
                   Exhibit 10.7)(1)

10.7          -    +1993 Stock Incentive Plan, as amended. (Originally filed
                   as Exhibit 10.8)(1)

10.8          -    +1993 Employee Stock Purchase Plan. (Originally filed as
                   Exhibit 10.9)(1)

10.9          -    +1993 Director Stock Option Plan, as amended. 

10.10         -    +Stock Option Plan of August 1, 1992. (Originally filed as
                   Exhibit 10.11)(1)

10.11         -    +Incentive Stock Option Plan of January 1, 1985. 
                   (Originally filed as Exhibit 10.12)(1)

10.12         -    +Stock Option Agreement, dated July 23, 1987, by and between
                   the Registrant and Mr. William M. Scranton. (Originally
                   filed as Exhibit 10.13)(1)

10.13         -    +Non-Qualified Employee Option Agreement, dated July 23, 
                   1987, by and between the Registrant and Mr. Barry R. Gorsun.
                   (Originally filed as Exhibit 10.14)(1)

10.14         -    +Stock Option Agreement, Dated July 1, 1984, by and between 
                   the Registrant and Mr. Robert A. Degan. (Originally filed 
                   as Exhibit 10.15)(1)

10.15         -    +Employment Agreement, dated April 3, 1993, by and between 
                   the Registrant and Thomas A. St. Germain. (Originally filed
                   as Exhibit 10.16)(1)

10.16         -    +Agreement, dated April 30, 1991, by and between the 
                   Registrant and Barry R. Gorsun. (Originally filed as 
                   Exhibit 10.17)(1)

10.17         -    +Promissory Note, dated February 12, 1993, by 
                   Barry R. Gorsun. (Originally filed as Exhibit 10.18)(1)

10.18         -    Promissory Note, dated April 1, 1991, by Summa Four, Ltd.
                   (Originally filed as Exhibit 10.19)(1)

10.19         -    +Promissory Note and amendment thereto, dated April 11, 
                   1989, by John T. Boatwright. (Originally filed as Exhibit 
                   10.20)(1)

10.20         -    Letter Agreement, dated October 15, 1992, by and between the
                   Registrant and Fleet Bank of Massachusetts, N.A., as 
                   modified. (Originally filed as Exhibit 10.21)(1)

10.21         -    Customer Purchase Agreement, dated November 20, 1992, by and
                   between the Registrant and Sprint/United Management Company.
                   (Originally filed as Exhibit 10.22)(1)

10.22         -    Specialty Switches Contract, dated March 13, 1992, by and 
                   between the Registrant and AT&T, Inc. (Originally filed as 
                   Exhibit 10.23)(1)

10.23         -    Customer Purchase Agreement, dated September 11, 1991, by 
                   and between the Registrant and United States Advanced 
                   Networks. (Originally filed as Exhibit 10.24)(1)

10.24         -    Customer Purchase Agreement, dated October 10, 1990, by and 
                   between the Registrant and Unisys Corporation. (Originally
                   filed as Exhibit 10.25)(1)

10.25         -    Resale Agreement, dated November 5, 1992, by and between the
                   Registrant and IBM Canada Ltd. (Originally filed as 
                   Exhibit 10.26)(1)
    
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                                 EXHIBIT INDEX                      

   
      10.26 - Agreement, dated October 14, 1992, by and between the Registrant
              and Claircom Communications Group, L.P. (Originally filed as
              Exhibit 10.27)(1)                       

      10.27 - Release, Settlement and License Agreement, dated November 2, 1992,
              by and among the Registrant, Omnitel Corporation, Aspect
              Telecommunications Corporation and Richard L. Scully. 
              (Originally filed as Exhibit 10.28)(1)

      10.28 - License Agreement, dated December 1, 1983, by and between the
              Registrant and Industrial Programming, Inc. (Originally filed as 
              Exhibit 10.29)(1)

      10.29 - Product Development and Licensing Agreement, dated January 19,
              1990, by and between the Registrant and The Telephone Connection,
              Inc. (Originally filed as Exhibit 10.30)(1)

      10.30 - +Letter Agreement, dated June 16, 1993, by and between the
              Registrant and Mr. Mel R. Ethem. (Originally filed as Exhibit 
              10.31)(1)
    

   
      10.31 - +Severance and Settlement Agreement and Release, dated August 8,
              1994, by and between the Registrant and James J. Fiedler.
              (Originally filed as Exhibit 10.33)(4)
  
      10.32 - +Agreement, dated August 1, 1994, by and between the Registrant
              and Barry R. Gorsun. (Originally filed as Exhibit 10.34)(4)
  
      10.33 - Loan Modification Agreement, dated July 28, 1993, by and between
              the Registrant and Fleet Bank of Massachusetts, N.A. (Originally
              filed as Exhibit 10.32)(2)
  
      10.34 - Promissory Note, dated July 28, 1993, by and between the 
              Registrant and Fleet Bank of Massachusetts, N.A. (Originally 
              filed as Exhibit 10.33)(2)
  
      10.35 - Amendment, dated August 31, 1994, to Lease Agreement dated
              July 18, 1990 with Northern Manchester Trust. (3)

      10.36 - Amendment, dated August 2, 1994, to Letter Agreement dated
              October 15, 1992 by and between the Registrant and Fleet Bank of
              Massachusetts, N.A. (6)

      10.37 - +Employment Agreement, dated May 3, 1995, by and between the
              Registrant and Edward C. Callahan. (Originally filed as Exhibit 
              10.36)(7)

      10.38 - +Stock Option Agreement, dated October 16, 1995, by and between
              the Registrant and Edgar L. Brown, Jr. (Originally filed as 
              Exhibit 10.37)(7)

      10.39 - Amendment, dated August 23, 1995, to Lease Agreement dated
              July 18, 1990 with Northern Manchester Trust. (Originally filed 
              as Exhibit 10.38)(7)

      10.40 - Customer Purchase Agreement, dated March 19, 1996, by and between
              the Registrant and NewNet, Inc. (Originally filed as Exhibit 
              10.39)(7)

      10.41 - +1996 Management Incentive Compensation Plan. (Originally filed 
              as Exhibit 10.40)(7)

      10.42 - +1995 Stock Option Plan.

      10.43 - Amendment, dated August 24, 1995, to Letter Agreement dated
              October 15, 1992 by and between the Registrant and Fleet Bank of
              Massachusetts, N.A.

      11    - Statement Regarding Computation of Per Share Earnings. (7)
   
      21    - Subsidiaries of the Registrant. (7)
   
      23    - Consent of Coopers & Lybrand. (7)
    


   
(1)  Incorporation herein by reference to the Registrant's Registration
     Statement on Form S-1 (File No. 33-66602), as declared effective by the
     Commission on September 23, 1993.

(2)  Incorporation herein by reference to the Registrant's Amendment No. 2 to
     its Annual Report on Form 10-K/A for the fiscal year ended March 31, 1994 
     filed with the Commission on June 19, 1998.

(3)  Incorporation herein by reference to the Registrant's Annual Report on Form
     10-K for the fiscal year ended March 31, 1995, filed with the Commission
     on June 27, 1995.

(4)  Incorporation herein by reference to the Registrant's Amendment No. 1 to
     its Annual Report on Form 10-K/A for the fiscal year ended March 31, 1995,
     filed with the Commission on May 9, 1997.

+    Management contract or compensatory plan or arrangement filed as an exhibit
     pursuant to Item 14(c) of this report.

(5)  Incorporation herein by reference to the Registrant's report on Form 8-K
     filed with the Commission on March 6, 1995.

(6)  Incorporation herein by reference to the Registrant's Amendment No. 2 to
     its Annual Report on Form 10-K/A for the fiscal year ended March 31, 1995
     as filed with the Commission on June 19, 1998

(7)  Incorporation herein by reference to the Registrant's Annual Report on
     Form 10-K for the fiscal year ended March 31, 1996 filed with the
     Commission on June 17, 1996.
    

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                                  SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the Registrant has duly caused this amendment to the
report to be signed on its behalf by the undersigned, thereunto duly authorized.



Dated: June 19, 1998                         Summa Four, Inc.



                                        By:  /s/ Jeffrey A. Weber
                                             ------------------------
                                             Jeffrey A. Weber
                                             Vice President and
                                             Chief Financial Officer