<PAGE>

                                                                  EXHIBIT  10.76

                             1998 STOCK OPTION PLAN
                             ----------------------

                          (As Amended on May 13, 1999)



     1.  Purposes of the Plan.  The purposes of this Stock Option Plan are to
         --------------------
attract and retain the best available personnel for positions of substantial
responsibility, to provide additional incentive to the Employees and Consultants
of the Company and to promote the success of the Company's business.

          Options granted hereunder may be either Incentive Stock Options (as
defined under Section 422 of the Code) or Nonstatutory Stock Options, at the
discretion of the Board and as reflected in the terms of the written option
agreement.

     2.  Definitions.  As used herein, the following definitions shall apply:
         -----------

          (a) "Administrator" shall mean the Board or any of its Committees
               -------------
appointed pursuant to Section 4 of the Plan.

          (b) "Affiliate" shall mean an entity other than a Subsidiary (as
               ---------
defined below) in which the Company owns an equity interest.

          (c) "Applicable Laws" shall have the meaning set forth in Section 4(a)
               ---------------
below.

          (d) "Board" shall mean the Board of Directors of the Company.
               -----

          (e) "Code" shall mean the Internal Revenue Code of 1986, as amended.
               ----

          (f) "Committee" shall mean the Committee appointed by the Board of
               ---------
Directors in accordance with Section 4(a) of the Plan, if one is appointed.

          (g) "Common Stock" shall mean the Common Stock of the Company.
               ------------

          (h) "Company" shall mean Vertel Corporation, a California corporation.
               -------

          (i) "Consultant" means any person, including an advisor, who is
               ----------
engaged by the Company or any Parent, Subsidiary or Affiliate to render services
and is compensated for such services, and any director of the Company whether
compensated for such services or not, so long as a director's eligibility is not
precluded by Applicable Laws.

          (j) "Continuous Status as an Employee or Consultant" shall mean the
               ----------------------------------------------
absence of any interruption or termination of service as an Employee or
Consultant.  Continuous Status as an Employee or Consultant shall not be
considered interrupted in the case of sick leave, military leave, or any other
leave of absence approved by the Administrator; provided that such leave is
                                                --------
<PAGE>

for a period of not more than 90 days or reemployment upon the expiration of
such leave is guaranteed by contract or statute. For purposes of this Plan, a
change in status from an Employee to a Consultant or from a Consultant to an
Employee will not constitute a termination of employment.

          (k) "Director" shall mean a member of the Board.
               --------

          (l) "Employee" shall mean any person (including any Named Executive,
               --------
Officer or Director) employed by the Company or any Parent, Subsidiary or
Affiliate of the Company.  The payment by the Company of a director's fee to a
Director shall not be sufficient to constitute "employment" of such Director by
the Company.

          (m) "Exchange Act" shall mean the Securities Exchange Act of 1934, as
               ------------
amended.

          (n) "Fair Market Value" means, as of any date, the value of Common
     Stock determined as follows:

          (i)  If the Common Stock is listed on any established stock exchange
               or a national market system including without limitation the
               National Association of Securities Dealers, Inc. Automated
               Quotation System ("NASDAQ") Stock Market, its Fair Market Value
               shall be the closing price for such stock as quoted on such
               exchange or market for the immediately preceding trading date
               prior to the date of determination (if for a given day no sales
               were reported, the closing bid on that day shall be used), as
               such prices are reported in The Wall Street Journal or such other
               source as the Administrator deems reliable;

          (ii) If the Common Stock is quoted on the NASDAQ System (but not on
               the NASDAQ Stock Market) or regularly quoted by a recognized
               securities dealer but selling prices are not reported, its Fair
               Market Value shall be the average of the mean between the bid and
               asked prices for the Common Stock for the immediately preceding
               trading date before the date of determination;

         (iii) In the absence of an established market for the Common Stock, the
               Fair Market Value thereof shall be determined in good faith by
               the Administrator.

          (o) "Incentive Stock Option" shall mean an Option intended to qualify
               ----------------------
as an incentive stock option within the meaning of Section 422 of the Code, as
designated in the applicable written option agreement.

          (p) "Named Executive" shall mean any individual who, on the last day
               ---------------
of the Company's fiscal year, is the chief executive officer of the Company (or
is acting in such

                                      -2-
<PAGE>

capacity) or among the four highest compensated officers of the Company (other
than the chief executive officer). Such officer status shall be determined
pursuant to the executive compensation disclosure rules under the Exchange Act.

          (q) "Nonstatutory Stock Option" shall mean an Option not intended to
               -------------------------
qualify as an Incentive Stock Option, as designated in the applicable written
option agreement.

          (r) "Officer" shall mean a person who is an officer of the Company
               -------
within the meaning of Section 16 of the Exchange Act and the rules and
regulations promulgated thereunder.

          (s) "Option" shall mean a stock option granted pursuant to the Plan.
               ------

          (t) "Optioned Stock" shall mean the Common Stock subject to an Option.
               --------------

          (u) "Optionee" shall mean an Employee or Consultant who receives an
               --------
Option.

          (v) "Parent" shall mean a "parent corporation," whether now or
               ------
hereafter existing, as defined in Section 424(e) of the Code.

          (w) "Plan" shall mean this 1998 Stock Option Plan.
               ----

          (x) "Rule 16b-3" shall mean Rule 16b-3 promulgated under the Exchange
               ----------
Act as the same may be amended from time to time, or any successor provision.

          (y) "Share" shall mean a share of the Common Stock, as adjusted in
               -----
accordance with Section 14 of the Plan.

          (z) "Subsidiary" shall mean a "subsidiary corporation," whether now or
               ----------
hereafter existing, as defined in Section 424(f) of the Code.

     3.  Stock Subject to the Plan.  Subject to the provisions of Section 14 of
         -------------------------
the Plan, the maximum aggregate number of shares that may be optioned and sold
under the Plan is 7,700,000 shares of Common Stock.  The Shares may be
authorized, but unissued, or reacquired Common Stock.

     If an Option should expire or become unexercisable for any reason without
having been exercised in full, the unpurchased Shares that were subject thereto
shall, unless the Plan shall have been terminated, become available for future
grant under the Plan.  Notwithstanding any other provision of the Plan, shares
issued under the Plan and later repurchased by the Company shall not become
available for future grant under the Plan.

                                      -3-
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     4.  Administration of the Plan.
         --------------------------

          (a)  Composition of Administrator.
               ----------------------------

          (i) Multiple Administrative Bodies.  If permitted by Rule 16b-3, and
              ------------------------------
by the legal requirements relating to the administration of incentive stock
option plans, if any, of applicable securities laws and the Code (collectively,
the "Applicable Laws"), grants under the Plan may (but need not) be made by
     ---------------
different administrative bodies with respect to Directors, Officers who are not
directors and Employees who are neither Directors nor Officers.

          (ii) Administration with respect to Directors and Officers.  With
               -----------------------------------------------------
respect to grants of Options to Employees or Consultants who are also Officers
or Directors of the Company, grants under the Plan shall be made by (A) the
Board, if the Board may make grants under the Plan in compliance with Rule 16b-3
and Section 162(m) of the Code as it applies so as to qualify grants of Options
to Named Executives as performance-based compensation, or (B) a Committee
designated by the Board to make grants under the Plan, which Committee shall be
constituted in such a manner as to permit grants under the Plan to comply with
Rule 16b-3, to qualify grants of Options to Named Executives as performance-
based compensation under Section 162(m) of the Code and otherwise so as to
satisfy the Applicable Laws.

          (iii)  Administration with respect to Other Persons.  With respect to
                 --------------------------------------------
grants of Options to Employees or Consultants who are neither Directors nor
Officers of the Company, the Plan shall be administered by (A) the Board or (B)
a Committee designated by the Board, which Committee shall be constituted in
such a manner as to satisfy the Applicable Laws.

          (iv) General.  If a Committee has been appointed pursuant to
               -------
subsection (ii) or (iii) of this Section 4(a), such Committee shall continue to
serve in its designated capacity until otherwise directed by the Board.  From
time to time the Board may increase the size of any Committee and appoint
additional members thereof, remove members (with or without cause) and appoint
new members in substitution therefor, fill vacancies (however caused) and remove
all members of a Committee and thereafter directly administer the Plan, all to
the extent permitted by the Applicable Laws and, in the case of a Committee
appointed under subsection (ii), to the extent permitted by Rule 16b-3 and to
the extent required under Section 162(m) of the Code to qualify grants of
Options to Named Executives as performance-based compensation.

          (b) Powers of the Administrator.  Subject to the provisions of the
              ---------------------------
Plan and in the case of a Committee, the specific duties delegated by the Board
to such Committee, the Administrator shall have the authority, in its
discretion:

                  (i) to determine the Fair Market Value of the Common Stock, in
accordance with Section 2(n) of the Plan;

                  (ii) to select the Employees and Consultants to whom Options
may from time to time be granted hereunder;

                                      -4-
<PAGE>

                  (iii) to determine whether and to what extent Options are
granted hereunder;

                  (iv) to determine the number of shares of Common Stock to be
covered by each such award granted hereunder;

                  (v) to approve forms of agreement for use under the Plan;

                  (vi) to determine the terms and conditions, not inconsistent
with the terms of the Plan, of any award granted hereunder (including, but not
limited to, the share price and any restriction or limitation, or any vesting
acceleration or waiver of forfeiture restrictions regarding any Option and/or
the shares of Common Stock relating thereto, based in each case on such factors
as the Administrator shall determine, in its sole discretion);

                  (vii) to reduce the exercise price of any Option to the then
current Fair Market Value if the Fair Market Value of the Common Stock covered
by such Option shall have declined since the date the Option was granted.

          (c) Effect of Administrator's Decision.  All decisions, determinations
              ----------------------------------
and interpretations of the Administrator shall be final and binding on all
Optionees and any other holders of any Options.

     5.  Eligibility.
         -----------

          (a) Recipients of Grants.  Nonstatutory Stock Options may be granted
              --------------------
to Employees and Consultants.  Incentive Stock Options may be granted only to
Employees, provided, however, that Employees of an Affiliate shall not be
           --------  -------
eligible to receive Incentive Stock Options.  An Employee or Consultant who has
been granted an Option may, if he or she is otherwise eligible, be granted an
additional Option or Options.

          (b) Type of Option.  Each Option shall be designated in the written
              --------------
option agreement as either an Incentive Stock Option or a Nonstatutory Stock
Option.  However, notwithstanding such designations, to the extent that the
aggregate Fair Market Value of Shares with respect to which Incentive Stock
Options are exercisable for the first time by an Optionee during any calendar
year (under all plans of the Company or any Parent or Subsidiary) exceeds
$100,000, such excess Options shall be treated as Nonstatutory Stock Options.
For purposes of this Section 5(b), Incentive Stock Options shall be taken into
account in the order in which they were granted, and the Fair Market Value of
the Shares shall be determined as of the time the Option with respect to such
Shares is granted.

          (c) No Employment Rights.  The Plan shall not confer upon any Optionee
              --------------------
any right with respect to continuation of employment or consulting relationship
with the Company, nor shall it interfere in any way with his or her right or the
Company's right to terminate his or her employment or consulting relationship at
any time, with or without cause.

                                      -5-
<PAGE>

     6.  Term of Plan.  The Plan shall become effective upon its approval by the
         ------------
shareholders of the Company as described in Section 20 of the Plan.  It shall
continue in effect for a term of ten (10) years unless sooner terminated under
Section 16 of the Plan.

     7.  Term of Option.  The term of each Option shall be the term stated in
         --------------
the Option Agreement; provided, however, that in the case of an Incentive Stock
                      --------  -------
Option, the term shall be no more than ten (10) years from the date of grant
thereof or such shorter term as may be provided in the Option Agreement.  In the
case of an Incentive Stock Option granted to an Optionee who, at the time the
Option is granted, owns stock representing more than ten percent (10%) of the
voting power of all classes of stock of the Company or any Parent or Subsidiary,
the term of the Option shall be five (5) years from the date of grant thereof or
such shorter term as may be provided in the Option Agreement.

     8.  Limitation on Grants to Employees.  Subject to adjustment as provided
         ---------------------------------
in this Plan, the maximum number of Shares which may be subject to Options
granted to any one Employee under this Plan for any fiscal year of the Company
shall be 1,000,000.

     9.  Option Exercise Price and Consideration.
         ---------------------------------------

          (a) Exercise Price.  The per Share exercise price for the Shares to be
              --------------
issued pursuant to exercise of an Option shall be such price as is determined by
the Administrator, but shall be subject to the following:

              (i) In the case of an Incentive Stock Option

                 (A) granted to an Employee who, at the time of the grant of
such Incentive Stock Option, owns stock representing more than ten percent (10%)
of the voting power of all classes of stock of the Company or any Parent or
Subsidiary, the per Share exercise price shall be no less than 110% of the Fair
Market Value per Share on the date of grant; or

                 (B) granted to any other Employee, the per Share exercise price
shall be no less than 100% of the Fair Market Value per Share on the date of
grant.

              (ii) In the case of a Nonstatutory Stock Option

                 (A) granted to a person who, at the time of the grant of such
Option, is a Named Executive of the Company, the per share Exercise Price shall
be no less than 100% of the Fair Market Value on the date of grant; or

                 (B) granted to any person other than a Named Executive, the per
Share exercise price shall be the price determined by the Administrator.

          (b) Permissible Consideration.  The consideration to be paid for the
              -------------------------
Shares to be issued upon exercise of an Option, including the method of payment,
shall be determined by the Administrator (and, in the case of an Incentive Stock
Option, shall be determined at the time of grant) and may consist entirely of
(1) cash, (2) check, (3) promissory note, (4) other Shares that (x) in the case
of Shares acquired upon exercise of an Option either have been owned

                                      -6-
<PAGE>

by the Optionee for more than six months on the date of surrender or were not
acquired, directly or indirectly, from the Company, and (y) have a Fair Market
Value on the date of surrender equal to the aggregate exercise price of the
Shares as to which said Option shall be exercised, (5) authorization from the
Company to retain from the total number of Shares as to which the Option is
exercised that number of Shares having a Fair Market Value on the date of
exercise equal to the exercise price for the total number of Shares as to which
the Option is exercised, (6) delivery of a properly executed exercise notice
together with irrevocable instructions to a broker to deliver promptly to the
Company the amount of sale or loan proceeds required to pay the exercise price,
(7) any combination of the foregoing methods of payment, or (8) such other
consideration and method of payment for the issuance of Shares to the extent
permitted under Applicable Laws. In making its determination as to the type of
consideration to accept, the Administrator shall consider if acceptance of such
consideration may be reasonably expected to benefit the Company.

     10.  Exercise of Option.
          ------------------

          (a) Procedure for Exercise; Rights as a Shareholder.  Any Option
              -----------------------------------------------
granted hereunder shall be exercisable at such times and under such conditions
as determined by the Administrator, including performance criteria with respect
to the Company and/or the Optionee, and as shall be permissible under the terms
of the Plan.

          An Option may not be exercised for a fraction of a Share.

          An Option shall be deemed to be exercised when written notice of such
exercise has been given to the Company in accordance with the terms of the
Option by the person entitled to exercise the Option and full payment for the
Shares with respect to which the Option is exercised has been received by the
Company.  Full payment may, as authorized by the Administrator, consist of any
consideration and method of payment allowable under Section 9(b) of the Plan.
Until the issuance (as evidenced by the appropriate entry on the books of the
Company or of a duly authorized transfer agent of the Company) of the stock
certificate evidencing such Shares, no right to vote or receive dividends or any
other rights as a shareholder shall exist with respect to the Optioned Stock,
notwithstanding the exercise of the Option.  The Company shall issue (or cause
to be issued) such stock certificate promptly upon exercise of the Option.  No
adjustment will be made for a dividend or other right for which the record date
is prior to the date the stock certificate is issued, except as provided in
Section 14 of the Plan.

          Exercise of an Option in any manner shall result in a decrease in the
number of Shares which thereafter may be available, both for purposes of the
Plan and for sale under the Option, by the number of Shares as to which the
Option is exercised.

          (b) Termination of Status as an Employee or Consultant.  In the event
              --------------------------------------------------
of termination of an Optionee's Continuous Status as an Employee or Consultant,
such Optionee may, but only within three (3) months (or such other period of
time, not exceeding three (3) months in the case of an Incentive Stock Option or
six (6) months in the case of a Nonstatutory Stock Option, as is determined by
the Administrator, with such determination in the case of an Incentive Stock
Option being made at the time of grant of the Option) after the date of such

                                      -7-
<PAGE>

termination (but in no event later than the date of expiration of the term of
such Option as set forth in the Option Agreement), exercise his or her Option to
the extent that he or she was entitled to exercise it at the date of such
termination.  To the extent that the Optionee was not entitled to exercise the
Option at the date of such termination, or if the optionee does not exercise
such Option (which he or she was entitled to exercise) within the time specified
herein, the Option shall terminate.

          (c) Disability of Optionee.  Notwithstanding Section 10(b) above, in
              ----------------------
the event of termination of an Optionee's Continuous Status as an Employee or
Consultant as a result of his or her total and permanent disability (as defined
in Section 22(e)(3) of the Code), he or she may, but only within six (6) months
(or such other period of time not exceeding twelve (12) months as is determined
by the Administrator, with such determination in the case of an Incentive Stock
Option being made at the time of grant of the Option) from the date of such
termination (but in no event later than the date of expiration of the term of
such Option as set forth in the Option Agreement), exercise his or her Option to
the extent he or she was entitled to exercise it at the date of such
termination.  To the extent that he or she was not entitled to exercise the
Option at the date of termination, or if he does not exercise such Option (which
he was entitled to exercise) within the time specified herein, the Option shall
terminate.

          (d) Death of Optionee.  In the event of the death of an Optionee:
              -----------------

             (i) during the term of the Option who is at the time of his death
an Employee or Consultant of the Company and who shall have been in Continuous
Status as an Employee or Consultant since the date of grant of the Option, the
Option may be exercised, at any time within six (6) months (or such other period
of time, not exceeding twelve (12) months, as is determined by the
Administrator, with such determination in the case of an Incentive Stock Option
being made at the time of grant of the Option) following the date of death (but
in no event later than the date of expiration of the term of such Option as set
forth in the Option Agreement), by the Optionee's estate or by a person who
acquired the right to exercise the Option by bequest or inheritance but only to
the extent of the right to exercise that would have accrued had the Optionee
continued living and remained in Continuous Status as an Employee or Consultant
twelve (12) months (or such other period of time as is determined by the
Administrator as provided above) after the date of death, subject to the
limitation set forth in Section 5(b); or

          (ii) within three (3) months (or such other period of time not
exceeding three (3) months as is determined by the Administrator, with such
determination in the case of an Incentive Stock Option being made at the time of
grant of the Option) after the termination of Continuous Status as an Employee
or Consultant, the Option may be exercised, at any time within six (6) months
following the date of death (but in no event later than the date of expiration
of the term of such Option as set forth in the Option Agreement), by the
Optionee's estate or by a person who acquired the right to exercise the Option
by bequest or inheritance, but only to the extent of the right to exercise that
had accrued at the date of termination.

          (e) Extension of Exercise Period.  The Administrator shall have full
              ----------------------------
power and authority to extend the period of time for which an option is to
remain exercisable following termination of an Optionee's Continuous Status as
an Employee or Consultant from the periods

                                      -8-
<PAGE>

set forth in Sections 10(b), 10(c) and 10(d) above or in the Option Agreement to
such greater time as the Board shall deem appropriate, provided, that in no
                                                       --------
event shall such option be exercisable later than the date of expiration of the
term of such Option as set forth in the Option Agreement.

          (f) Rule 16b-3.  Options granted to persons subject to Section 16(b)
              ----------
of the Exchange Act must comply with Rule 16b-3 and shall contain such
additional conditions or restrictions as may be required thereunder to qualify
for the maximum exemption from Section 16 of the Exchange Act with respect to
Plan transactions.

     11.  Withholding Taxes.  As a condition to the exercise of Options granted
          -----------------
hereunder, the Optionee shall make such arrangements as the Administrator may
require for the satisfaction of any federal, state, local or foreign withholding
tax obligations that may arise in connection with the exercise, receipt or
vesting of such Option.  The Company shall not be required to issue any Shares
under the Plan until such obligations are satisfied.

     12.  Stock Withholding to Satisfy Withholding Tax Obligations.  At the
          --------------------------------------------------------
discretion of the Administrator, Optionees may satisfy withholding obligations
as provided in this paragraph.  When an Optionee incurs tax liability in
connection with an Option which tax liability is subject to tax withholding
under applicable tax laws, and the Optionee is obligated to pay the Company an
amount required to be withheld under applicable tax laws, the Optionee may
satisfy the withholding tax obligation by one or some combination of the
following methods:  (a) by cash payment, or (b) out of Optionee's current
compensation, or (c) if permitted by the Administrator, in its discretion, by
surrendering to the Company Shares that (i) in the case of Shares previously
acquired from the Company, have been owned by the Optionee for more than six
months on the date of surrender, and (ii) have a fair market value on the date
of surrender equal to or less than Optionee's marginal tax rate times the
ordinary income recognized, or (d) by electing to have the Company withhold from
the Shares to be issued upon exercise of the Option that number of Shares having
a fair market value equal to the amount required to be withheld.  For this
purpose, the fair market value of the Shares to be withheld shall be determined
on the date that the amount of tax to be withheld is to be determined (the "Tax
                                                                            ---
Date").
----

          Any surrender by an Officer or Director of previously owned Shares to
satisfy tax withholding obligations arising upon exercise of an Option must
comply with the applicable provisions of Rule 16b-3.

          All elections by an Optionee to have Shares withheld to satisfy tax
withholding obligations shall be made in writing in a form acceptable to the
Administrator and shall be subject to the following restrictions:

          (a) the election must be made on or prior to the applicable Tax Date;

          (b) once made, the election shall be irrevocable as to the particular
Shares of the Option as to which the election is made; and

                                      -9-
<PAGE>

          (c) all elections shall be subject to the consent or disapproval of
the Administrator.

          In the event the election to have Shares withheld is made by an
Optionee and the Tax Date is deferred under Section 83 of the Code because no
election is filed under Section 83(b) of the Code, the Optionee shall receive
the full number of Shares with respect to which the Option is exercised but such
Optionee shall be unconditionally obligated to tender back to the Company the
proper number of Shares on the Tax Date.

     13.  Non-Transferability of Options.  Options may not be sold, pledged,
          ------------------------------
assigned, hypothecated, transferred, or disposed of in any manner other than by
will or by the laws of descent or distribution; provided that the Administrator
                                                --------
may in its discretion grant transferable Nonstatutory Stock Options pursuant to
agreements specifying (i) the manner in which such Nonstatutory Stock Options
are transferable; (ii) that any such transfer shall be limited to the following
recipients: a charitable trust established by the Optionee, a living trust
established by the Optionee or a member of Optionee's immediate family; and
(iii) that any such transfer shall be subject to the Applicable Laws.  The
designation of a beneficiary by an Optionee will not constitute a transfer.  An
Option may be exercised, during the lifetime of the Optionee, only by the
Optionee or a transferee permitted by this Section 13.

     14.  Adjustments Upon Changes in Capitalization; Corporate Transactions.
          ------------------------------------------------------------------

          (a) Adjustment.  Subject to any required action by the shareholders of
              ----------
the Company, the number of shares of Common Stock covered by each outstanding
Option, the number of shares of Common Stock that have been authorized for
issuance under the Plan but as to which no Options have yet been granted or
which have been returned to the Plan upon cancellation or expiration of an
Option, the maximum number of shares of Common Stock for which Options may be
granted to any employee under Section 8 of the Plan, and the price per share of
Common Stock covered by each such outstanding Option, shall be proportionately
adjusted for any increase or decrease in the number of issued shares of Common
Stock resulting from a stock split, reverse stock split, stock dividend,
combination or reclassification of the Common Stock, or any other increase or
decrease in the number of issued shares of Common Stock effected without receipt
of consideration by the Company; provided, however, that conversion of any
convertible securities of the Company shall not be deemed to have been "effected
without receipt of consideration."  Such adjustment shall be made by the
Administrator, whose determination in that respect shall be final, binding and
conclusive.  Except as expressly provided herein, no issuance by the Company of
shares of stock of any class, or securities convertible into shares of stock of
any class, shall affect, and no adjustment by reason thereof shall be made with
respect to, the number or price of shares of Common Stock subject to an Option.

          (b) Corporate Transactions.  In the event of the proposed dissolution
              ----------------------
or liquidation of the Company, each Option will terminate immediately prior to
the consummation of such proposed action, unless otherwise provided by the
Administrator.  The Administrator may, in the exercise of its sole discretion in
such instances, declare that any Option shall terminate as of a date fixed by
the Administrator and give each Optionee the right to exercise his

                                      -10-
<PAGE>

or her Option as to all or any part of the Optioned Stock, including Shares as
to which the Option would not otherwise be exercisable. In the event of a
proposed sale of all or substantially all of the assets of the Company, or the
merger of the Company with or into another corporation, each Option shall be
assumed or an equivalent option shall be substituted by such successor
corporation or a parent or subsidiary of such successor corporation, unless the
Administrator determines, in the exercise of its sole discretion and in lieu of
such assumption or substitution, that the Optionee shall have the right to
exercise the Option as to some or all of the Optioned Stock, including Shares as
to which the Option would not otherwise be exercisable. If the Administrator
makes an Option exercisable in lieu of assumption or substitution in the event
of a merger or sale of assets, the Administrator shall notify the Optionee that
the Option shall be exercisable for a period of fifteen (15) days from the date
of such notice, and the Option will terminate upon the expiration of such
period.

     15.  Time of Granting Options.  The date of grant of an Option shall, for
          ------------------------
all purposes, be the date on which the Administrator makes the determination
granting such Option or such other date as is determined by the Administrator;
provided however that in the case of any Incentive Stock Option, the grant date
-------- -------
shall be the later of the date on which the Administrator makes the
determination granting such Incentive Stock Option or the date of commencement
of the Optionee's employment relationship with the Company.  Notice of the
determination shall be given to each Employee or Consultant to whom an Option is
so granted within a reasonable time after the date of such grant.

     16.  Amendment and Termination of the Plan.
          -------------------------------------

          (a) Amendment and Termination.  The Board may amend or terminate the
              -------------------------
Plan from time to time in such respects as the Board may deem advisable;
provided that, the following revisions or amendments shall require approval of
the shareholders of the Company in the manner described in Section 20 of the
Plan:

                  (i) any increase in the number of Shares subject to the Plan
available for grant as incentive stock options, other than an adjustment under
Section 15 of the Plan;

                  (ii) any change in the designation of the class of persons
eligible to be granted Options; or

                  (iii) any change in the limitation on grants to employees as
described in Section 8 of the Plan or other changes which would require
shareholder approval to qualify Options granted hereunder as performance-based
compensation under Section 162(m) of the Code.

          (b) Shareholder Approval.  If any amendment requiring shareholder
              --------------------
approval under Section 16(a) of the Plan is made subsequent to the first
registration of any class of equity securities by the Company under Section 12
of the Exchange Act, such shareholder approval shall be solicited as described
in Section 20 of the Plan.

                                      -11-
<PAGE>

          (c) Effect of Amendment or Termination.  Any such amendment or
              ----------------------------------
termination of the Plan shall not affect Options already granted and such
Options shall remain in full force and effect as if this Plan had not been
amended or terminated, unless mutually agreed otherwise between the Optionee and
the Board, which agreement must be in writing and signed by the Optionee and the
Company.

     17.  Conditions Upon Issuance of Shares.  Shares shall not be issued
          ----------------------------------
pursuant to the exercise of an Option unless the exercise of such Option and the
issuance and delivery of such Shares pursuant thereto shall comply with all
relevant provisions of law, including, without limitation, the Securities Act of
1933, as amended, the Exchange Act, the rules and regulations promulgated
thereunder, and the requirements of any stock exchange upon which the Shares may
then be listed, and shall be further subject to the approval of counsel for the
Company with respect to such compliance.

     As a condition to the exercise of an Option, the Company may require the
person exercising such Option to represent and warrant at the time of any such
exercise that the Shares are being purchased only for investment and without any
present intention to sell or distribute such Shares if, in the opinion of
counsel for the Company, such a representation is required by any of the
aforementioned relevant provisions of law.

     18.  Reservation of Shares.  The Company, during the term of this Plan,
          ---------------------
will at all times reserve and keep available such number of Shares as shall be
sufficient to satisfy the requirements of the Plan.  The inability of the
Company to obtain authority from any regulatory body having jurisdiction, which
authority is deemed by the Company's counsel to be necessary to the lawful
issuance and sale of any Shares hereunder, shall relieve the Company of any
liability in respect of the failure to issue or sell such Shares as to which
such requisite authority shall not have been obtained.

     19.  Agreements.  Options shall be evidenced by written agreements in such
          ----------
form as the Board shall approve.

     20.  Shareholder Approval.  Continuance of the Plan shall be subject to
          --------------------
approval by the shareholders of the Company within twelve (12) months before or
after the date the Plan is adopted.  Such shareholder approval shall be obtained
in the manner and to the degree required under applicable federal and state law
and the rules of any stock exchange upon which the Shares are listed.

                                      -12-
<PAGE>

                               VERTEL CORPORATION
                             STOCK OPTION AGREEMENT
                             ----------------------

                            (1998 Stock Option Plan)
                            ------------------------

     1.  Grant of Option.  Vertel Corporation, a California corporation (the
         ---------------
"Company"), hereby grants to the Optionee named in the Notice of Stock Option
--------
Grant attached to this Agreement ("Optionee"), an option (the "Option") to
                                   --------                    ------
purchase the total number of shares of Common Stock (the "Shares") set forth in
                                                          ------
the Notice of Stock Option Grant, at the exercise price per share set forth in
the Notice of Stock Option Grant (the "Exercise Price") subject to the terms,
                                       --------------
definitions and provisions of the 1998 Stock Option Plan (the "Plan") adopted by
                                                               ----
the Company, which is incorporated in this Agreement by reference.  In the event
of a conflict between the terms of the Plan and the terms of this Agreement, the
terms of the Plan shall govern.  Unless otherwise defined in this Agreement, the
terms used in this Agreement shall have the meanings defined in the Plan.

     To the extent designated an Incentive Stock Option in the Notice of Stock
Option Grant, this Option is intended to qualify as an Incentive Stock Option as
defined in Section 422 of the Internal Revenue Code of 1986, as amended (the
"Code") and, to the extent not so designated, this Option is intended to be a
-----
Nonstatutory Stock Option.

     2.  Exercise of Option.  This Option shall be exercisable during its term
         ------------------
in accordance with the Vesting Schedule set out in the Notice of Stock Option
Grant and with the provisions of Sections 9 and 10 of the Plan as follows:

          (a)  Right to Exercise.
               -----------------

               (i) This Option may not be exercised for a fraction of a share.

               (ii) In the event of Optionee's death, disability or other
termination of employment, the exercisability of the Option is governed by
Sections 6, 7 and 8 below, subject to the limitations contained in paragraphs
(iii) and (iv) below.

               (iii) In no event may this Option be exercised after the date of
expiration of the term of this Option as set forth in the Notice of Stock Option
Grant.

               (iv) If designated an Incentive Stock Option in the Notice of
Stock Option Grant, in the event that the Shares subject to this Option (and all
other Incentive Stock Options granted to Optionee by the Company or any Parent
or Subsidiary) that vest in any calendar year have an aggregate fair market
value (determined for each Share as of the Date of Grant of the option covering
such Share) in excess of $100,000, the Shares in excess of $100,000 shall be
treated as subject to a Nonstatutory Stock Option, in accordance with Section 5
of the Plan.

                                      -13-
<PAGE>

          (b)  Method of Exercise.
               ------------------

               (i) This Option shall be exercisable by delivering to the Company
a written notice of exercise (in the form attached as Exhibit A) which shall
                                                      ---------
state the election to exercise the Option, the number of Shares in respect of
which the Option is being exercised, and such other representations and
agreements as to the holder's investment intent with respect to such Shares of
Common Stock as may be required by the Company pursuant to the provisions of the
Plan. Such written notice shall be signed by Optionee and shall be delivered in
person or by certified mail to the Secretary of the Company. The written notice
shall be accompanied by payment of the Exercise Price. This Option shall be
deemed to be exercised upon receipt by the Company of such written notice
accompanied by the Exercise Price.

               (ii) As a condition to the exercise of this Option, Optionee
agrees to make adequate provision for federal, state or other tax withholding
obligations, if any, which arise upon the exercise of the Option or disposition
of Shares, whether by withholding, direct payment to the Company, or otherwise.

               (iii) No Shares will be issued pursuant to the exercise of an
Option unless such issuance and such exercise shall comply with all relevant
provisions of law and the requirements of any stock exchange upon which the
Shares may then be listed. Assuming such compliance, for income tax purposes the
Shares shall be considered transferred to Optionee on the date on which the
Option is exercised with respect to such Shares.

     3.  Optionee's Representations.  In the event the Shares purchasable
         --------------------------
pursuant to the exercise of this Option have not been registered under the
Securities Act of 1933, as amended (the "Securities Act"), at the time this
                                         --------------
Option is exercised, Optionee shall, if required by the Company, concurrently
with the exercise of all or any portion of this Option, deliver to the Company
an investment representation statement in customary form, a copy of which is
available for Optionee's review from the Company upon request.

     4.  Method of Payment.  Payment of the Exercise Price shall be by any of
         -----------------
the following, or a combination of the following, at the election of Optionee:
(a) cash; (b) check; (c) surrender of other Shares of Common Stock of the
Company that (i) either have been owned by Optionee for more than six (6) months
on the date of surrender or were not acquired, directly or indirectly, from the
Company, and (ii) have a Fair Market Value on the date of surrender equal to the
aggregate exercise price of the Shares as to which said Option shall be
exercised; (d) authorization from the Company to retain from the total number of
Shares as to which the Option is exercised that number of Shares having a Fair
Market value on the date of exercise equal to the exercise price for the total
number of Shares as to which the Option is exercised; or (e) if there is a
public market for the Shares and they are registered under the Securities Act,
delivery of a properly executed exercise notice together with irrevocable
instructions to a broker to deliver promptly to the Company the amount of sale
or loan proceeds required to pay the exercise price.

     5.  Restrictions on Exercise.  This Option may not be exercised until such
         ------------------------
time as the Plan has been approved by the shareholders of the Company, or if the
issuance of such Shares

                                      -14-
<PAGE>

upon such exercise or the method of payment of consideration for such shares
would constitute a violation of any applicable federal or state securities or
other law or regulation, including any rule under Part 207 of Title 12 of the
Code of Federal Regulations ("Regulation G") as promulgated by the Federal
                              ------------
Reserve Board. As a condition to the exercise of this Option, the Company may
require Optionee to make any representation and warranty to the Company as may
be required by any applicable law or regulation.

     6.  Termination of Relationship.  In the event of termination of Optionee's
         ---------------------------
Continuous Status as an Employee or Consultant, Optionee may, to the extent
otherwise so entitled at the date of such termination (the "Termination Date"),
                                                            ----------------
exercise this Option during the Termination Period set out in the Notice of
Stock Option Grant.  To the extent that Optionee was not entitled to exercise
this Option at the date of such termination, or if Optionee does not exercise
this Option within the time specified in the Notice of Stock Option Grant, the
Option shall terminate.

     7.  Disability of Optionee.  Notwithstanding the provisions of Section 6
         ----------------------
above, in the event of termination of Optionee's Continuous Status as an
Employee or Consultant as a result of total and permanent disability (as defined
in Section 22(e)(3) of the Code), Optionee may, but only within six (6) months
from the date of termination of employment (but in no event later than the date
of expiration of the term of this Option as set forth in Section 10 below),
exercise the Option to the extent otherwise so entitled at the date of such
termination.  To the extent that Optionee was not entitled to exercise the
Option at the date of termination, or if Optionee does not exercise such Option
(to the extent otherwise so entitled) within the time specified in this
Agreement, the Option shall terminate.

     8.  Death of Optionee.  In the event of the death of Optionee:
         -----------------

          (a) during the term of this Option and while an Employee of the
Company and having been in Continuous Status as an Employee or Consultant since
the date of grant of the Option, the Option may be exercised, at any time within
six (6) months following the date of death (but in no event later than the date
of expiration of the term of this Option as set forth in Section 10 below), by
Optionee's estate or by a person who acquired the right to exercise the Option
by bequest or inheritance, but only to the extent of the right to exercise that
would have accrued had Optionee continued living and remained in Continuous
Status as an Employee or Consultant three (3) months after the date of death,
subject to the limitation contained in Section 2(i)(d) above in the case of an
Incentive Stock Option; or

          (b) within thirty (30) days after the termination of Optionee's
Continuous Status as an Employee or Consultant, the Option may be exercised, at
any time within six (6) months following the date of death (but in no event
later than the date of expiration of the term of this Option as set forth in
Section 10 below), by Optionee's estate or by a person who acquired the right to
exercise the Option by bequest or inheritance, but only to the extent of the
right to exercise that had accrued at the date of termination.

     9.  Non-Transferability of Option.  This Option may not be transferred in
         -----------------------------
any manner otherwise than by will or by the laws of descent or distribution.
The designation of a

                                      -15-
<PAGE>

beneficiary does not constitute a transfer. An Option may be exercised during
the lifetime of Optionee only by Optionee or a transferee permitted by this
section. The terms of this Option shall be binding upon the executors,
administrators, heirs, successors and assigns of Optionee.

     10.  Term of Option.  This Option may be exercised only within the term set
          --------------
out in the Notice of Stock Option Grant, and may be exercised during such term
only in accordance with the Plan and the terms of this Option.

     11.  No Additional Employment Rights.  Optionee understands and agrees that
          -------------------------------
the vesting of Shares pursuant to the Vesting Schedule is earned only by
continuing as an Employee or Consultant at the will of the Company (not through
the act of being hired, being granted this Option or acquiring Shares under this
Agreement).  Optionee further acknowledges and agrees that nothing in this
Agreement, nor in the Plan which is incorporated in this Agreement by reference,
shall confer upon Optionee any right with respect to continuation as an Employee
or Consultant with the Company, nor shall it interfere in any way with his or
her right or the Company's right to terminate his or her employment or
consulting relationship at any time, with or without cause.

     12.  Tax Consequences.  Optionee acknowledges that he or she has read the
          ----------------
brief summary set forth below of certain federal tax consequences of exercise of
this Option and disposition of the Shares under the law in effect as of the date
of grant.  OPTIONEE UNDERSTANDS THAT THIS SUMMARY IS NECESSARILY INCOMPLETE, AND
THE TAX LAWS AND REGULATIONS ARE SUBJECT TO CHANGE.  OPTIONEE SHOULD CONSULT HIS
OR HER OWN TAX ADVISER BEFORE EXERCISING THIS OPTION OR DISPOSING OF THE SHARES.

          (a) Exercise of Incentive Stock Option.  If this Option is an
              ----------------------------------
Incentive Stock Option, there will be no regular federal income tax liability
upon the exercise of the Option, although the excess, if any, of the fair market
value of the Shares on the date of exercise over the Exercise Price will be
treated as an item of alternative minimum taxable income for federal tax
purposes and may subject Optionee to the alternative minimum tax in the year of
exercise.

          (b) Exercise of Nonstatutory Stock Option.  If this Option does not
              -------------------------------------
qualify as an Incentive Stock Option, Optionee may incur regular federal income
tax liability upon the exercise of the Option.  Optionee will be treated as
having received compensation income (taxable at ordinary income tax rates) equal
to the excess, if any, of the fair market value of the Shares on the date of
exercise over the Exercise Price.  In addition, if Optionee is an employee of
the Company, the Company will be required to withhold from Optionee's
compensation or collect from Optionee and pay to the applicable taxing
authorities an amount equal to a percentage of this compensation income at the
time of exercise.

          (c) Disposition of Shares.  If this Option is an Incentive Stock
              ---------------------
Option and if Shares transferred pursuant to the Option are held for more than
one year after exercise and more than two years after the Date of Grant, any
gain realized on disposition of the Shares will be treated as long-term capital
gain for federal income tax purposes.  If Shares purchased under an Incentive
Stock Option are disposed of before the end of either of such two holding
periods, then

                                      -16-
<PAGE>

any gain realized on such disposition will be treated as compensation income
(taxable at ordinary income rates) to the extent of the excess, if any, of the
lesser of (i) the fair market value of the Shares on the date of exercise, or
(ii) the sales proceeds, over the Exercise Price. If this Option is a
Nonstatutory Stock Option, then gain realized on the disposition of Shares will
be treated as long-term or short-term capital gain depending on whether or not
the disposition occurs more than one year after the exercise date. In the case
of either an Incentive Stock Option or a Nonstatutory Stock Option, the long-
term capital gain will be taxed for federal income tax and alternative minimum
tax purposes as a maximum rate of 28% if the Shares are held more than one year
but less than 18 months after exercise and at 20% if the Shares are held more
than 18 months after exercise.

          (d) Notice of Disqualifying Disposition.  If the Option granted to
              -----------------------------------
Optionee in this Agreement is an Incentive Stock Option, and if Optionee sells
or otherwise disposes of any of the Shares acquired pursuant to the Incentive
Stock Option on or before the later of (i) the date two years after the Date of
Grant, or (ii) the date one year after transfer of such Shares to Optionee upon
exercise of the Incentive Stock Option, Optionee shall notify the Company in
writing within thirty (30) days after the date of any such disposition.
Optionee agrees that Optionee may be subject to income tax withholding by the
Company on the compensation income recognized by Optionee from the early
disposition by payment in cash or out of the current earnings paid to Optionee.

     13.  Signature.  This Stock Option Agreement shall be deemed executed by
          ---------
the Company and Optionee upon execution by such parties of the Notice of Stock
Option Grant attached to this Stock Option Agreement.


                  [Remainder of page left intentionally blank]

                                      -17-
<PAGE>

                                   EXHIBIT A
                                   ---------

                               NOTICE OF EXERCISE
                               ------------------

To:      Vertel Corporation
Attn:    Stock Option Administrator
Subject: Notice of Intention to Exercise Stock Option
         --------------------------------------------

     This is official notice that the undersigned ("Optionee") intends to
                                                    --------
exercise Optionee's option to purchase __________ shares of Vertel Corporation
Common Stock, under and pursuant to the Company's 1998 Stock Option Plan and the
Stock Option Agreement dated ___________, as follows:

          Grant Number:  ________________________________

          Date of Purchase:  ____________________________

          Number of Shares:  _____________________________

          Purchase Price:  _______________________________

          Method of Payment
          of Purchase Price:  ____________________________


     Social Security No.:  _______________________________

     The shares should be issued as follows:

          Name:________________________________

          Address:_____________________________

                  _____________________________

                  _____________________________


          Signed:
                  _____________________________

          Date:
                  _____________________________