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                                                                   EXHIBIT 99.16


                               ACT NETWORKS, INC.
                                 188 CAMINO RUIZ
                           CAMARILLO, CALIFORNIA 93012




                                  June 3, 1996





ACT Executive Officers
ACT Networks, Inc.
188 Camino Ruiz
Camarillo, California 93012

                  Re:  Outstanding Option to Purchase Shares of
                       ACT Networks, Inc. (the "Company")

Dear Executive Officer:

                  Our records indicate that you are currently the holder of the
installment non-statutory stock options evidenced on the attached Notices of
Grant issued under the Company's 1995 Stock Option/Stock Issuance Plan.

                  At present your option is structured so that it will become
exercisable as to twenty-four percent (24%) of the option shares one (1) year
after the Vesting Commencement Date and as to the balance of the option shares
in a series of equal monthly installments over the next succeeding thirty-eight
(38) months, provided you remain in the service of the Company.

                  To provide you with greater flexibility in timing the exercise
of your option, the Company's Board of Directors has recently established an
option acceleration program for its executive officers who have received options
since the Company's initial public offering in May of 1995. Under the program,
your option will be made fully and immediately exercisable for any and all of
the Company's shares not yet purchased thereunder. However, to assure that the
vesting schedule presently in effect under your installment option is
maintained, all shares purchased under the accelerated option will be subject to
repurchase by the Company at the original exercise price upon your termination
of employment.

                  This repurchase right will lapse in a series of annual and
monthly installments as your employment with the Company continues so that the
purchased shares will become vested in accordance with the same vesting schedule
presently in effect under your installment option.
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ACT Executive Officers
June 3, 1996                                                              Page 2



                  The specific terms of the new program may be summarized as
follows:

                  1. Exercise of Option. Your accelerated option may be
exercised in whole or in part at any time before the expiration date specified
above, provided you continue in the Company's employ. Should your employment
terminate for any reason other than death or permanent disability, you will have
only a three (3)-month period following termination in which to exercise your
option. Should you die or become permanently disabled while the option is
outstanding, the three (3)-month exercise period will be extended to twelve (12)
months. Under no circumstances, however, may your option be exercised after the
expiration date specified above.

                  2. Repurchase Rights. The shares you purchase under the
accelerated option will be subject to repurchase by the Company should you
terminate employment before you acquire a vested interest in the shares.
Accordingly, upon your termination of employment, the Company will have the
right to repurchase your unvested shares at the original exercise price. This
repurchase right will lapse, and you will vest in your option shares, in
accordance with the following schedule: (i) twenty-four percent (24%) of the
option shares will vest upon your completion of one (1) year of service with the
Company measured from the Vesting Commencement Date and (ii) the balance of the
option shares will vest in a series of equal monthly installments upon your
completion of each additional month of service with the Company over the next
thirty-eight (38) months thereafter. Should you decide to exercise your
accelerated option for unvested shares, you must at that time sign and deliver a
Stock Purchase Agreement to the Company as a condition to the purchase of your
shares. Any shares which are subject to the Company's repurchase right at the
time of purchase will be held in escrow by the Company until you subsequently
vest in such shares. Any shares in which you are vested at the time of purchase
will not be subject to repurchase by the Company, and a certificate for those
shares will be delivered to you as soon as practicable following exercise of the
option.

                  3. Vesting. You will lose no vesting credit under your
accelerated option. The Company's repurchase right will lapse, and your shares
will be released from escrow, in installments at exactly the same time your
option would become exercisable for those shares in accordance with the
installment schedule presently in effect thereunder. Accordingly, the repurchase
right and escrow requirement will apply only to shares for which your option
would not otherwise at the time be exercisable in the absence of the
acceleration program. Shares in which you are already vested will not be subject
to repurchase and will not be held in escrow. As a result, the program offers
you complete flexibility in timing the exercise of your option while you remain
an employee of the Company without the loss of any benefits under your present
option.

                  4. Remaining Terms of Option. Except for the acceleration of
exercisability and the required delivery of the Stock Purchase Agreement upon
exercise, no other terms or conditions of your present option will be changed as
a result of the 
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ACT Executive Officers
June 3, 1996                                                              Page 3



acceleration program, and all these terms and conditions will continue in full
force and effect.

                  Attached to this letter are the following documents which will
govern the terms of your immediately exercisable options: (i) Form of Stock
Option Agreement, (ii) Form of Stock Purchase Agreement and (iii) Form of Notice
of Grant (collectively the "New Option Documents").

                  Enclosed you will find a Certificate of Acknowledgment. Please
acknowledge your participation in the program, as well as the receipt of the New
Option Documents, by executing and returning the Certificate to Jan Wolfe.

                  You should attach this letter and the New Option Documents to
your old stock option agreements in order to evidence the acceleration of your
option and the new forms. Acceleration will automatically become effective as of
May 21, 1996.

                  Should you have any questions concerning the program or the
conditions applicable to your accelerated option, please direct them to the
undersigned or Jan Wolfe.

                                Very truly yours,


                                _________________________________________
                                Martin Shum
                                President and Chief Executive Officer

Enclosure
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                          CERTIFICATE OF ACKNOWLEDGMENT

                  I hereby acknowledge receipt of the Company's letter of June
3, 1996 indicating my eligibility for participation in a special option
acceleration program. I have read the letter and understand that participation
in the program is entirely voluntary. I understand that my outstanding stock
option under the Company's 1995 Stock Option/Stock Issuance Plan will be
automatically converted, effective May 21, 1996, into a fully and immediately
exercisable option. I further understand that the shares I purchase under the
accelerated option may be subject to repurchase by the Company and held in
escrow.

                  I also acknowledge receipt of (i) a Form of Notice of Grant,
(ii) a Form of Stock Option Agreement and (iii) a Form of Stock Purchase
Agreement that will govern the terms and conditions applicable to all my stock
options granted from May 10, 1995 to May 21, 1996.

                  In response to the letter, I have signed below to acknowledge
my participation in the program.


                                    Signed:________________________________


                                    Dated:_________________________________
