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

                                 ---------------

   
                                  FORM 10-K/A
    

                  FOR ANNUAL AND TRANSITION REPORTS PURSUANT TO
                          SECTIONS 13 OR 15(d) OF THE
                        SECURITIES EXCHANGE ACT OF 1934

 (MARK ONE)

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

                     FOR THE FISCAL YEAR ENDED JUNE 30, 1998

                                       OR

[ ]  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 0-25740


                               ACT NETWORKS, INC.
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                              --------------------

          DELAWARE                                              77-0152144
(STATE OR OTHER JURISDICTION                                 (I.R.S. EMPLOYER
OF INCORPORATION OR ORGANIZATION)                            IDENTIFICATION NO.)


                  188 CAMINO RUIZ, CAMARILLO, CALIFORNIA 93012
               (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES) (ZIP CODE)

       REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE: (805) 388-2474


        SECURITIES REGISTERED PURSUANT TO SECTION 12(B) OF THE ACT: NONE

           SECURITIES REGISTERED PURSUANT TO SECTION 12(G) OF THE ACT:

                                  COMMON STOCK
                                (Title of Class)

        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 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. [ ]

   
        Based on the closing sale price on Nasdaq National Market on August 31,
1998, the aggregate market value of the voting stock held by non-affiliates of
the registrant was $46,502,400.
    

        As of August 31, 1998, there were 9,376,480 shares of Common Stock
outstanding.

                       DOCUMENTS INCORPORATED BY REFERENCE
                                      NONE

================================================================================

<PAGE>   2

Net sales

        The Company classifies its sales as either international or domestic.
International sales are, in general, shipments to locations outside the United
States, regardless of the end-user's or the customer's location. Domestic sales
are, in general, shipments to locations within the United States, even if the
end-user or customer is located outside the United States. As the Company sells
primarily through resellers, the Company does not know with certainty the
location of the end-user. The Company believes that a majority of sales that it
classifies as domestic are shipped to end-users outside the United States.

        The Company also classifies its sales by customer. In general, the
end-users of the Company's products are either enterprise customers who acquire
the Company's products for use in their own network or service providers who use
the Company's products to provide telecommunications services to third parties.
Service providers include alternate service providers (such as wholesale
long-distance carriers and call-back operators), value added network services
providers, competitive local exchange carriers, incumbent local exchange
carriers, competitive access providers, Internet Service Providers and
Interexchange Carriers. The Company's NetPerformer products may be used by both
enterprise customers and service providers. The Company's ServiceXchange
products are designed primarily for the service provider market. As the Company
does not intend to actively promote many of its former products which have,
historically, accounted for a majority of the Company's net sales, the Company's
net sales may be adversely impacted in the near term. The Company has in the
past, and may in the future, encounter decreased sales as a result of product
transitions.

   
        Net sales increased 11.8% to $55.0 million for the fiscal year ended
June 30, 1998 from $49.2 million for the fiscal year ended June 30, 1997. This
increase was primarily as a result of increased domestic sales of the Company's
products as well as sales of products from businesses acquired in fiscal 1997
and 1998. Increases in sales to Europe and the Asia Pacific region were offset
by decreases in sales to South America. Net sales to the Asia Pacific region
decreased substantially from the first two quarters of the fiscal year ending
June 30, 1998 to quarters three and four of current fiscal year. For the fiscal
year ended June 30, 1998, sales to enterprise customers were approximately $35.7
million, or 64.9%, and sales to service providers were approximately $19.3
million, or 35.1%. The following table sets forth, for the fiscal periods
indicated, the percentages of total net sales represented by domestic and
international sales.
    

<TABLE>
<CAPTION>
                                                       Fiscal Year Ended
                                               --------------------------------
                                               June 30, 1998      June 30, 1997
                                               -------------      -------------
<S>                                            <C>                 <C>
            Domestic Sales                          36.2%             25.3%
            International Sales                     63.8              74.7
                                                   -----             -----
                                                   100.0%            100.0%
                                                   =====             =====
</TABLE>

        Net sales increased 73.1% to $49.2 million for the fiscal year ended
June 30, 1997 from $28.4 million for the fiscal year ended June 30, 1996 due to
increased unit sales of the Company's Frame Relay access products. Included in
net sales is $2.5 million attributable to sales of products from businesses
acquired in fiscal 1997. For the fiscal year ended June 30, 1997, sales to
enterprise customers were approximately $41.2 million, or 83.8%, and sales to
service providers were approximately $8.0 million, or 16.2%. For the fiscal year
ended June 30, 1996, sales to enterprise customers were approximately $23
million, or 5.4%, and sales to service providers were approximately $5.4
million, or 19.0%.

        The two categories of customers operate either terrestrial or wireless
networks. For the fiscal year ended June 30, 1997, sales of products into
terrestrial and wireless networks were approximately $36 million, or 73.2%, and
$13.2 million, or 26.8%, respectively. For the fiscal year ended June 30, 1996,
sales of products into terrestrial and wireless networks were approximately
$18.4 million, or 64.8%, and $10 million, or 35.2%, respectively.

Gross Profit

        Gross profit represents net sales less the cost of goods sold, which
includes cost of materials, manufacturing overhead costs and direct labor
expenses. The Company's gross profit was $25.1 million, or 45.6% of net sales,
for the fiscal year ended June 30, 1998. The Company's gross profit was $27.7
million, or 56.4% of net sales, for the fiscal year ended June 30, 1997. Cost of
goods sold for the year ended June 30, 1998 includes charges of $3.7 million to
write-down the carrying value of inventory due to the de-emphasis or
discontinuation of certain product lines. Without these charges, gross profit
for the fiscal year ended June 30, 1998 would have been $28.7 million, or 52.2 %
of net sales. The decrease in gross profit as a percentage of sales was
primarily attributable to decreases in average sales prices due to competitive
pressure. Management anticipates continued downward pressure on gross profit as
a percentage of sales, particularly as the Company pursues OEM opportunities
that typically produce lower gross margins.

        The Company's gross profit was $27.7 million, or 56.4% of net sales, for
the fiscal year ended June 30, 1997. The Company's gross profit was $14.4
million, or 50.7% of net sales, for the fiscal year ended June 30, 1996. Fiscal
1996 included a $700,000 charge for obsolete inventory that was taken to

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<PAGE>   3

                                    PART III

ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT

EXECUTIVE OFFICERS AND DIRECTORS

        The following table sets forth certain information concerning the
executive officers and directors of the Company as of August 31, 1998.

   
<TABLE>
<CAPTION>
  NAME                               AGE     POSITION
  ----                               ---     --------
<S>                                  <C>     <C>
  Andre de Fusco                     40      President and Chief Executive Officer
  Melvin L. Flowers                  45      Chief Financial Officer and Vice
                                             President, Finance and Administration
  Alain Gravel                       39      Vice President, Engineering
  Christopher F. Perna               34      Vice President, Sales
  Mike T. Zeile                      34      Vice President, Marketing
  H. Peter Staab                     51      Chief Technology Officer
  Brig. Gen. Harold R. Johnson(1)(2) 75      Director
  William Ambrose (1)(2)             40      Director
  Archibald J. McGill (1)(2)         67      Director
  Frederick W. Gluck                 63      Director
</TABLE>
    

-----------
(1)     Member of the Compensation Committee.
(2)     Member of the Audit Committee.

        Andre de Fusco was appointed President and Chief Executive Officer in
July 1998. Previously Mr. de Fusco held several positions with the Company,
including the position of Vice President and General Manager of the Company's
Broadband Network Services subsidiary from August 1997 to June 1998, Vice
President, Strategic Planning and Business Development from December 1995 to
June 1998 and Vice President of Marketing from December 1994 to December 1995.
Mr. de Fusco was employed as Director of International Accounts and Director of
Business Development for Northern Telecom from 1991 to 1994 and as Vice
President of Marketing and President of MaxCom, a developer of electronic mail
systems, from 1984 to 1991.

        Melvin L. Flowers has served as Chief Financial Officer and Vice
President of Finance since July 1993 and as Vice President, Finance and
Administration since December 1995. Prior to joining the Company, Mr. Flowers
served as President and Chief Financial Officer of Pacific Earth Resources, an
ornamental horticultural company, from 1991 to 1993 and from 1989 to 1991,
respectively, and as Vice President and Chief Financial Officer of Spectramed
Incorporated, a medical device manufacturing company, from 1986 to 1989.

   
        Alain Gravel was appointed Vice President, Engineering in July 1998.
From November 1995 to July 1998, Mr. Gravel served as Vice President of Research
& Development, Data Products, Enterprise Network Systems. Mr. Gravel served as
Vice President of Research & Development of Presticom until the Company acquired
Presticom in November 1995. Mr. Gravel was a co-founder of Presticom and was
responsible for the development of the NetPerformer product line. He also served
on the Board of Directors of Presticom. Mr. Gravel was employed as the Software
Development Manager for Memotec from 1988 to 1989 and for Datagram, a developer
of statistical multiplexers, from 1984 to 1988.
    

        Christopher F. Perna was appointed Vice President, Sales in July 1998.
Previously, Mr. Perna was Vice President of Sales at ComCore Semiconductor based
in Calabasas, California, where he was responsible for worldwide sales and
application support from 1997 to 1998. Prior to ComCore, Mr. Perna was a
manufacturer sales representative at Jones & McGeoy Sales from 1994 to 1997, and
a district sales manager at Integrated Devices Technology from 1991 to 1994.

        Mike T. Zeile was appointed Vice President, Marketing in July 1998. Mr.
Zeile held the position of Vice President of Marketing at ComCore Semiconductor
from July 1997 to July 1998 where he managed all aspects of the Company's
marketing business as well as product management. Prior to joining ComCore, Mr.
Zeile worked at Sourcecom Corporation, where he led the definition of the
product platform that became the basis for ACT's new ServiceXchange product
family. Mr. Zeile has also held various senior management and marketing
positions at ADC Telecommunications from 1987 to 1997.

        H. Peter Staab was appointed Chief Technology Officer in July 1998. Mr.
Staab previously served as Vice President, Corporate Research and Development
from July 1997 to July 1998 and served as Vice President of Engineering from
June 1995 to July 1998. Before joining the Company, Mr. Staab was employed at
General DataComm as Director of Network Management and Systems from 1992 to 1995
and Director of Transmission Products from 1985 to 1992.


                                       24


<PAGE>   4

ITEM 11. EXECUTIVE COMPENSATION

EXECUTIVE COMPENSATION

        The following table sets forth the aggregate compensation paid by any
person for all services rendered in all capacities to the Company to the Chief
Executive Officer and to each of the four additional most highly compensated
executive officers (the "Named Executive Officers") for the fiscal year ended
June 30, 1996, 1997 and 1998. Except as indicated below, during fiscal year
1996, 1997, and 1998, no Named Executive Officer received other compensation in
excess of the lesser of $50,000 or 10% of such officer's compensation, nor did
any such officer receive any restricted stock award, stock appreciation right or
payment under any long term incentive plan.

                           SUMMARY COMPENSATION TABLE

   
<TABLE>
<CAPTION>
                                                                                  LONG-TERM
                                                   ANNUAL COMPENSATION           COMPENSATION
                                            -------------------------------      -------------
                                            FISCAL                 BONUS/         UNDERLYING
NAME AND PRINCIPAL POSITIONS                 YEAR   SALARY      COMMISSION($)     OPTIONS (#)
-----------------------------                ----   ------      -------------    -------------
<S>                                         <C>     <C>          <C>              <C>
Martin Shum (1)..........................   1998    $270,000                      100,000(6)
                                            1997     225,000
                                            1996     190,000                      251,500(3)(4)

Linda Carlson (1)........................   1998     140,000        28,000         20,000(6)
                                            1997     100,000       101,092
                                            1996     117,553        87,200         38,429(3)(4)(5)

John W. Tucker (1).......................   1998     140,000        52,000         20,000(6)
                                            1997     100,000       121,576
                                            1996     102,510        65,714         67,286(3)(4)

Melvin L. Flowers .......................   1998     150,000                       20,000(6)
   Chief Financial Officer and Vice         1997     140,000
   President, Finance and Administration    1996     120,000                       68,429(3)(4)

Andre de Fusco (2).......................   1998     140,000                       20,000(6)
   Vice President, Strategic Planning       1997     140,000
   and and Business Development             1996     123,335         7,677         54,286(3)(4)
</TABLE>
    

-----------
(1) The above-named officer is no longer employed by the Company.

(2) Mr. de Fusco is the current Chief Executive Officer and President of the
    Company.

(3) Each of the Named Executive Officers were granted the following stock
    options on August 1, 1995 pursuant to the Company's 1995 Option Bonus
    Program at an exercise price of $16.50: Mr. Shum, 24,000; Ms. Carlson,
    1,429; Mr. Tucker, 2,286; Mr. Flowers, 3,429; and Mr. de Fusco, 2,286. The
    options are immediately exercisable with any unvested shares acquired under
    such option being subject to repurchase by the Company, at the exercise
    price, upon termination of the optionee's service with the Company, and vest
    according to the following schedule ("Standard Vesting"): twenty-four
    percent (24%) of the shares vest upon completion of one year following the
    vesting commencement and the balance will vest at a rate of two percent (2%)
    per full month of employment thereafter.

(4) Each of the Named Executive Officers were granted the following Stock
    Options on September 19, 1996 at an exercise price of $13.00: Mr. Shum,
    227,500; Ms. Carlson, 7,000; Mr. Tucker, 65,000; Mr. Flowers, 65,000, and
    Mr. de Fusco, 52,000. The options were immediately exercisable with any
    unvested shares acquired under such option being subject to repurchase by
    the Company, at the exercise price, upon termination of the optionee's
    service with the Company, and is subject to the Company's Standard Vesting.

(5) Ms. Carlson was elected to serve as the Company's Vice President, Worldwide
    Sales on December 11, 1995 and granted a stock option to purchase 30,000
    shares of the Company's Common Stock. The option is immediately exercisable
    with any unvested shares acquired under such option being subject to
    repurchase by the Company, at the exercise price, upon termination of the
    Optionee's service with the Company and is subject to the Company's Standard
    Vesting.

(6) Each of the Named Executive Officers were granted the Stock Options on
    December 3, 1997 at an exercise price of $7.69. Mr. Shum and Mr. Flowers
    were granted options pursuant to the Company's 1997 Stock Incentive Plan and
    Ms. Carlson, Mr. Tucker and Mr. de Fusco were granted options pursuant to
    the Company's 1995 Option Bonus Program. The options were immediately
    exercisable with any unvested shares acquired under such option being
    subject to repurchase by the Company, at the exercise price, upon
    termination of the optionee's service with the Company, and is subject to
    the Company's Standard Vesting.

                                       26
<PAGE>   5

12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT.

        The following table sets forth certain information with respect to the
beneficial ownership of the Company's Common Stock as of August 31, 1998 by (i)
each person known by the Company to beneficially own more than 5% of the
outstanding shares of Common Stock, (ii) each of the Company's directors, (iii)
each of the Named Executive Officers, and (iv) all directors and executive
officers of the Company as a group:

   
<TABLE>
<CAPTION>
                                                                  SHARES BENEFICIALLY
                                                                       OWNED(1)
DIRECTORS, FIVE PERCENT STOCKHOLDERS, NAMED EXECUTIVE             --------------------
OFFICERS AND DIRECTORS AND OFFICERS AS A GROUP                    NUMBER       PERCENT
--------------------------------------------------------          --------------------
<S>                                                               <C>          <C>
Heartland Advisors (2)..................................          810,000       8.6%
Kingdom Capital Management Corporation (2)..............          582,200       6.2
Andre de Fusco (3)......................................          405,135       4.1
Melvin L. Flowers (4)...................................           31,929        *
Alain Gravel (5)........................................           57,621        *
Christopher F. Perna (6)................................           90,000        *
Mike T. Zeile (7).......................................           90,000        *
H. Peter Staab (8)......................................           97,446       1.0
Brig. Gen. H. R. Johnson (9)............................           29,714        *
William W. Ambrose (10).................................           49,155        *
Archibald J. McGill (11)................................           56,857        *
Frederick W. Gluck (12).................................           52,000        *
All directors and executive officers as a
   group (10 persons) (13)..............................          959,857       9.4%
Martin Shum (14) (15)...................................          536,212       5.5%
John Tucker (14) (16)...................................           63,904        *
Linda Carlson (14) (17).................................           25,941        *
</TABLE>
    

-----------

  *  Less than 1%.

 (1) Unless otherwise indicated, the persons named in the table have sole voting
     and sole investment power with respect to all shares beneficially owned,
     subject to community property laws where applicable.

 (2) Based upon information contained in unofficial databases as of June 30,
     1998.

 (3) Includes 401,000 shares issuable upon exercise of immediately exercisable
     options, of which 73,440 shares will be vested within 60 days from August
     31, 1998.

 (4) Includes 10,000 shares issuable upon exercise of immediately exercisable
     options, of which 10,000 shares will be vested within 60 days from August
     31, 1998.

 (5) Includes 42,000 shares issuable upon exercise of immediately exercisable
     options, of which 17,400 shares will be vested within 60 days from August
     31, 1998.

 (6) Includes 90,000 shares issuable upon exercise of immediately exercisable
     options, of which no shares will be vested within 60 days from August 31,
     1998.

 (7) Includes 90,000 shares issuable upon exercise of immediately exercisable
     options, of which no shares will be vested within 60 days from August 31,
     1998.

 (8) Includes 94,000 shares issuable upon exercise of immediately exercisable
     options, of which 53,800 shares will be vested within 60 days from August
     31, 1998.

 (9) Includes 24,000 shares issuable upon exercise of immediately exercisable
     options, of which 14,000 shares will be vested within 60 days from August
     31, 1998.

(10) Includes 25,155 shares beneficially owned by Stone Silo Investments. Mr.
     Ambrose, as sole owner of Stone Silo Investments, may be deemed to have
     beneficial ownership of these shares. Also includes 24,000 shares issuable
     upon exercise of immediately exercisable options, of which 14,000 shares
     will be vested within 60 days from August 31, 1998.


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<PAGE>   6

                                   SIGNATURES

   
Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the Registrant has duly caused this Report to be signed on its
behalf by the undersigned, thereunto duly authorized, in the City of Camarillo,
State of California, on October 14, 1998.
    

                                       ACT NETWORKS, INC.


                                       By: /s/ ANDRE DE FUSCO
                                           ----------------------------------
                                           Andre De Fusco
                                           President and Chief Executive Officer


                                POWER OF ATTORNEY

        We, the undersigned officers and directors of ACT Networks, Inc., do
hereby constitute and appoint Andre de Fusco and Melvin L. Flowers, and each of
them, our true and lawful attorneys-in-fact and agents, each with full power of
substitution and resubstitution, for him and in his name, place and stead, in
any and all capacities, to sign any and all amendments to this Report, and to
file the same, with exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite or necessary to be done in
and about the premises, as fully to all intents and purposes as he might or
could do in person, hereby, ratifying and confirming all that each of said
attorneys-in-fact and agents, or his substitute or substitutes, may lawfully do
or cause to be done by virtue hereof.

        Pursuant to the requirements of the Securities Exchange Act of 1934,
this Report has been signed below by the following persons in the capacities and
on the dates indicated:

   
<TABLE>
<CAPTION>

Signature                                 Title                               Date
---------                                 -----                               ----
<S>                              <C>                                    <C>
/s/ Andre de Fusco               President and Chief Executive           October 14, 1998
-----------------------------    Officer
    Andre de Fusco


/s/ MELVIN L. FLOWERS            Vice President, Finance and             October 14, 1998
-----------------------------    Chief Financial Officer (principal
    Melvin L. Flowers            financial and accounting officer)


/s/ WILLIAM W. AMBROSE           Director                                October 14, 1998
-----------------------------
    William W. Ambrose


/s/ HAROLD R. JOHNSON            Director                                October 14, 1998
-----------------------------
    Harold R. Johnson


s/ ARCHIBALD J. MCGILL           Director                                October 14, 1998
-----------------------------
   Archibald J. McGill


/s/ Frederick W. Gluck           Director                                October 14, 1998
-----------------------------
    Frederick W. Gluck
</TABLE>
    


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