<PAGE>

                                                                     EXHIBIT 4.3

THIS WARRANT AND THE SHARES OF COMMON STOCK ISSUABLE UPON EXERCISE HEREOF HAVE
NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE
"SECURITIES ACT") OR ANY STATE SECURITIES LAWS AND MAY NOT BE SOLD, TRANSFERRED
OR OTHERWISE DISPOSED OF UNLESS REGISTERED UNDER THE SECURITIES ACT AND UNDER
APPLICABLE STATE SECURITIES LAWS OR VERTEL CORPORATION SHALL HAVE RECEIVED AN
OPINION OF ITS COUNSEL THAT REGISTRATION OF SUCH SECURITIES UNDER THE SECURITIES
ACT AND UNDER THE PROVISIONS OF APPLICABLE STATE SECURITIES LAWS IS NOT
REQUIRED.

                              WARRANT TO PURCHASE

                             SHARES OF COMMON STOCK

                                       OF

                               VERTEL CORPORATION


                            Expires August 31, 2006

No.: W-1                                               Number of Shares: 800,000
Date of Issuance: August 31, 2001


     FOR VALUE RECEIVED, subject to the provisions hereinafter set forth, the
undersigned, Vertel Corporation, a California corporation (together with its
successors and assigns, the "Issuer"), hereby certifies that SDS MERCHANT FUND,
                             ------
L.P. or its registered assigns is entitled to subscribe for and purchase, during
the period specified in this Warrant, up to Eight Hundred Thousand (800,000)
shares (subject to adjustment as hereinafter provided) of the duly authorized,
validly issued, fully paid and non-assessable Common Stock of the Issuer, at an
exercise price per share equal to the Warrant Price then in effect, subject,
however, to the provisions and upon the terms and conditions hereinafter set
forth.  Capitalized terms used in this Warrant and not otherwise defined herein
shall have the respective meanings specified in Section 9 hereof.

     1.  Term.  The right to subscribe for and purchase shares of Warrant Stock
         ----
represented hereby shall commence on the date of issuance of this Warrant and
shall expire at 5:00 p.m., eastern time, on August 31, 2006 (such period being
the "Term").
     ----

                                      -1-
<PAGE>

     2.  Method of Exercise Payment; Issuance of New Warrant; Transfer and
         -----------------------------------------------------------------
Exchange.
--------

     (a) Time of Exercise.  The purchase rights represented by this Warrant may
         ----------------
be exercised in whole or in part at any time and from time to time during the
Term.

     (b) Method of Exercise.  The Holder hereof may exercise this Warrant, in
         ------------------
whole or in part, by the surrender of this Warrant (with the exercise form
attached hereto duly executed) at the principal office of the Issuer, and by the
payment to the Issuer of an amount of consideration therefor equal to the
Warrant Price in effect on the date of such exercise multiplied by the number of
shares of Warrant Stock with respect to which this Warrant is then being
exercised, payable at such Holder's election (i) by certified or official bank
check or by wire transfer to an account designated by the Issuer, (ii) by
"cashless exercise" by surrender to the Issuer for cancellation of a portion of
this Warrant representing that number of unissued shares of Warrant Stock which
is equal to the quotient obtained by dividing (A) the product obtained by
multiplying the Warrant Price by the number of shares of Warrant Stock being
purchased upon such exercise by (B) the Per Share Market Value as of the date of
such exercise, or (iii) by a combination of the foregoing methods of payment
selected by the Holder of this Warrant.  In any case where the consideration
payable upon such exercise is being paid in whole or in part pursuant to the
provisions of clause (ii) of this subsection (b), such exercise shall be
accompanied by written notice from the Holder of this Warrant specifying the
manner of payment thereof and containing a calculation showing the number of
shares of Warrant Stock with respect to which rights are being surrendered
thereunder and the net number of shares to be issued after giving effect to such
surrender.

     (c) Issuance of Stock Certificates.  In the event of any exercise of the
         ------------------------------
rights represented by this Warrant in accordance with and subject to the terms
and conditions hereof, (i) certificates for the shares of Warrant Stock so
purchased shall be dated the date of such exercise and delivered to the Holder
hereof within a reasonable time, not exceeding three (3) Trading Days after such
exercise, and the Holder hereof shall be deemed for all purposes to be the
Holder of the shares of Warrant Stock so purchased as of the date of such
exercise, and (ii) unless this Warrant has expired, a new Warrant representing
the number of shares of Warrant Stock, if any, with respect to which this
Warrant shall not then have been exercised (less any amount thereof which shall
have been canceled in payment or partial payment of the Warrant Price as
hereinabove provided) shall also be issued to the Holder hereof at the Issuer's
expense within such time.

     (d) Transferability of Warrant.  Subject to Section 2(e), this Warrant may
         --------------------------
be transferred by a Holder without the consent of the Issuer.  If transferred
pursuant to this paragraph and subject to the provisions of subsection (e) of
this Section 2, this Warrant may be transferred on the books of the Issuer by
the Holder hereof in person or by duly authorized attorney, upon surrender of
this Warrant at the principal office of the Issuer, properly endorsed (by the
Holder executing an assignment in the form attached hereto) and upon payment of
any necessary transfer tax or other governmental charge imposed upon such
transfer.  This Warrant is exchangeable at the principal office of the Issuer
for Warrants for the purchase of the same aggregate number of shares of Warrant
Stock, each new Warrant to represent the right to purchase such number of shares
of Warrant Stock as the Holder hereof shall designate at the time

                                      -2-
<PAGE>

of such exchange. All Warrants issued on transfers or exchanges shall be dated
the Original Issue Date and shall be identical with this Warrant except as to
the number of shares of Warrant Stock issuable pursuant hereto.

     (e) Compliance with Securities Laws.
         --------------------------------

          (i)   The Holder of this Warrant, by acceptance hereof, acknowledges
     that this Warrant or the shares of Warrant Stock to be issued upon exercise
     hereof are being acquired solely for the Holder's own account and not as a
     nominee for any other party, and for investment, and that the Holder will
     not offer, sell or otherwise dispose of this Warrant or any shares of
     Warrant Stock to be issued upon exercise hereof except pursuant to an
     effective registration statement, or an exemption from registration, under
     the Securities Act and any applicable state securities laws.

          (ii)  Except as provided in paragraph (iii) below, this Warrant and
     all certificates representing shares of Warrant Stock issued upon exercise
     hereof shall be stamped or imprinted with a legend in substantially the
     following form:

          THIS WARRANT AND THE SHARES OF COMMON STOCK ISSUABLE UPON EXERCISE
          HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
          AMENDED (THE "SECURITIES ACT") OR ANY STATE SECURITIES LAWS AND MAY
          NOT BE SOLD, TRANSFERRED OR OTHERWISE DISPOSED OF UNLESS REGISTERED
          UNDER THE SECURITIES ACT AND UNDER APPLICABLE STATE SECURITIES LAWS OR
          VERTEL CORPORATION SHALL HAVE RECEIVED AN OPINION OF ITS COUNSEL THAT
          REGISTRATION OF SUCH SECURITIES UNDER THE SECURITIES ACT AND UNDER THE
          PROVISIONS OF APPLICABLE STATE SECURITIES LAWS IS NOT REQUIRED.

          (iii) The restrictions imposed by this subsection (e) upon the
     transfer of this Warrant or the shares of Warrant Stock to be purchased
     upon exercise hereof shall terminate (A) when such securities shall have
     been resold pursuant to an effective registration statement under the
     Securities Act, (B) upon the Issuer's receipt of an opinion of counsel, in
     form and substance reasonably satisfactory to the Issuer, addressed to the
     Issuer to the effect that such restrictions are no longer required to
     ensure compliance with the Securities Act and state securities laws or (C)
     upon the Issuer's receipt of other evidence reasonably satisfactory to the
     Issuer that such registration and qualification under the Securities Act
     and state securities laws are not required.  Whenever such restrictions
     shall cease and terminate as to any such securities, the Holder thereof
     shall be entitled to receive from the Issuer (or its transfer agent and
     registrar), without expense (other than applicable transfer taxes, if any),
     new Warrants (or, in the case of shares of Warrant Stock, new stock
     certificates) of like tenor not bearing the applicable legend required by
     paragraph (ii) above relating to the Securities Act and state securities
     laws.

                                      -3-
<PAGE>

     (f) Continuing Rights of Holder.  The Issuer will, at the time of or at any
         ---------------------------
time after each exercise of this Warrant, upon the request of the Holder hereof,
acknowledge in writing the extent, if any, of its continuing obligation to
afford to such Holder all rights to which such Holder shall continue to be
entitled after such exercise in accordance with the terms of this Warrant,
provided that if any such Holder shall fail to make any such request, the
--------
failure shall not affect the continuing obligation of the Issuer to afford such
rights to such Holder.

     3.  Stock Fully Paid; Reservation and Listing of Shares; Covenants.
         ---------------------------------------------------------------

     (a) Stock Fully Paid.  The Issuer represents, warrants, covenants and
         ----------------
agrees that all shares of Warrant Stock which may be issued upon the exercise of
this Warrant or otherwise hereunder will, upon issuance, be duly authorized,
validly issued, fully paid and non-assessable and free from all taxes, liens and
charges created by or through Issuer.  The Issuer further covenants and agrees
that during the period within which this Warrant may be exercised, the Issuer
will at all times have authorized and reserved for the purpose of the issue upon
exercise of this Warrant a sufficient number of shares of Common Stock to
provide for the exercise of this Warrant.

     (b) Reservation.  If any shares of Common Stock required to be reserved for
         -----------
issuance upon exercise of this Warrant or as otherwise provided hereunder
require registration or qualification with any governmental authority under any
federal or state law before such shares may be so issued, the Issuer will in
good faith use its best efforts as expeditiously as possible at its expense to
cause such shares to be duly registered or qualified.  If the Issuer shall list
any shares of Common Stock on any securities exchange or market it will, at its
expense, list thereon, maintain and increase when necessary such listing, of,
all shares of Warrant Stock from time to time issued upon exercise of this
Warrant or as otherwise provided hereunder, and, to the extent permissible under
the applicable securities exchange rules, all unissued shares of Warrant Stock
which are at any time issuable hereunder, so long as any shares of Common Stock
shall be so listed.  The Issuer will also so list on each securities exchange or
market, and will maintain such listing of, any other securities which the Holder
of this Warrant shall be entitled to receive upon the exercise of this Warrant
if at the time any securities of the same class shall be listed on such
securities exchange or market by the Issuer.

     (c) Covenants.  The Issuer shall not by any action including, without
         ---------
limitation, amending the Articles of Incorporation or the by-laws of the Issuer,
or through any reorganization, transfer of assets, consolidation, merger,
dissolution, issue or sale of securities or any other action, avoid or seek to
avoid the observance or performance of any of the terms of this Warrant, but
will at all times in good faith assist in the carrying out of all such terms and
in the taking of all such actions as may be necessary or appropriate to protect
the rights of the Holder hereof against dilution (to the extent specifically
provided herein) or impairment.  Without limiting the generality of the
foregoing, the Issuer will (i) not permit the par value, if any, of its Common
Stock to exceed the then effective Warrant Price, (ii) not amend or modify any
provision of the Articles of Incorporation or by-laws of the Issuer in any
manner that would adversely affect in any way the powers, preferences or
relative participating, optional or other special rights of the Common Stock or
which would adversely affect the rights of the Holders of

                                      -4-
<PAGE>

the Warrants, (iii) take all such action as may be reasonably necessary in order
that the Issuer may validly and legally issue fully paid and nonassessable
shares of Common Stock, free and clear of any liens, claims, encumbrances and
restrictions (other than as provided herein) upon the exercise of this Warrant,
and (iv) use its best efforts to obtain all such authorizations, exemptions or
consents from any public regulatory body having jurisdiction thereof as may be
reasonably necessary to enable the Issuer to perform its obligations under this
Warrant.

     (d) Loss, Theft, Destruction of Warrants.  Upon receipt of evidence
         ------------------------------------
satisfactory to the Issuer of the ownership of and the loss, theft, destruction
or mutilation of any Warrant and, in the case of any such loss, theft or
destruction, upon receipt of indemnity or security satisfactory to the Issuer
or, in the case of any such mutilation, upon surrender and cancellation of such
Warrant, the Issuer will make and deliver, in lieu of such lost, stolen,
destroyed or mutilated Warrant, a new Warrant of like tenor and representing the
right to purchase the same number of shares of Common Stock.

     4.  Adjustment of Warrant Price and Warrant Share Number.  The number of
         ----------------------------------------------------
shares of Common Stock for which this Warrant is exercisable, and the price at
which such shares may be purchased upon exercise of this Warrant, shall be
subject to adjustment from time to time as set forth in this Section 4. The
Issuer shall give the Holder notice of any event described below which requires
an adjustment pursuant to this Section 4 in accordance with Section 5.

     (a) Recapitalization, Reorganization, Reclassification, Consolidation,
         ------------------------------------------------------------------
Merger or Sale.
--------------

         (i)  In case the Issuer after the Original Issue Date shall do any of
the following (each, a "Triggering Event"): (a) consolidate with or merge
                        ----------------
into any other Person and the Issuer shall not be the continuing or surviving
corporation of such consolidation or merger, or (b) permit any other Person to
consolidate with or merge into the Issuer and the Issuer shall be the continuing
or surviving Person but, in connection with such consolidation or merger, any
Capital Stock of the Issuer shall be changed into or exchanged for Securities of
any other Person or cash or any other property, or (c) transfer all or
substantially all of its properties or assets to any other Person, or (d) effect
a capital reorganization or reclassification of its Capital Stock, then, and in
the case of each such Triggering Event, proper provision shall be made so that,
upon the basis and the terms and in the manner provided in this Warrant, the
Holder of this Warrant shall be entitled (x) upon the exercise hereof at any
time after the consummation of such Triggering Event, to the extent this Warrant
is not exercised prior to such Triggering Event, to receive at the Warrant Price
in effect at the time immediately prior to the consummation of such Triggering
Event in lieu of the Common Stock issuable upon such exercise of this Warrant
prior to such Triggering Event, the Securities, cash and property to which such
Holder would have been entitled upon the consummation of such Triggering Event
if such Holder had exercised the rights represented by this Warrant immediately
prior thereto, subject to adjustments (subsequent to such corporate action) as
nearly equivalent as possible to the adjustments provided for elsewhere in this
Section 4 or (y) to sell this Warrant (or, at such Holder's election, a portion
hereof) concurrently with the Triggering Event to the Person continuing after or
surviving such Triggering Event, or to the Issuer (if Issuer is the continuing
or surviving Person) at a sales price equal to the amount of

                                      -5-
<PAGE>

     cash, property and/or Securities to which a holder of the number of shares
     of Common Stock which would otherwise have been delivered upon the exercise
     of this Warrant would have been entitled upon the effective date or closing
     of any such Triggering Event (the "Event Consideration"), less the amount
                                        -------------------
     or portion of such Event Consideration having a fair value equal to the
     aggregate Warrant Price applicable to this Warrant or the portion hereof so
     sold.

          (ii)  Notwithstanding anything contained in this Warrant to the
     contrary, the Issuer will not effect any Triggering Event unless, prior to
     the consummation thereof, each Person (other than the Issuer) which may be
     required to deliver any Securities, cash or property upon the exercise of
     this Warrant as provided herein shall assume, by written instrument
     delivered to, and reasonably satisfactory to, the Holder of this Warrant,
     (A) the obligations of the Issuer under this Warrant (and if the Issuer
     shall survive the consummation of such Triggering Event, such assumption
     shall be in addition to, and shall not release the Issuer from, any
     continuing obligations of the Issuer under this Warrant) and (B) the
     obligation to deliver to such Holder such shares of Securities, cash or
     property as, in accordance with the foregoing provisions of this subsection
     (a), such Holder shall be entitled to receive, and such Person shall have
     similarly delivered to such Holder an opinion of counsel for such Person,
     which counsel shall be reasonably satisfactory to such Holder, stating that
     this Warrant shall thereafter continue in full force and effect and the
     terms hereof (including, without limitation, all of the provisions of this
     subsection (a)) shall be applicable to the Securities, cash or property
     which such Person may be required to deliver upon any exercise of this
     Warrant or the exercise of any rights pursuant hereto.

          (iii) If with respect to any Triggering Event, the Holder of this
     Warrant has exercised its right as provided in clause (y) of subparagraph
     (i) of this subsection (a) to sell this Warrant or a portion thereof, the
     Issuer agrees that as a condition to the consummation of any such
     Triggering Event the Issuer shall secure such right of Holder to sell this
     Warrant to the Person continuing after or surviving such Triggering Event
     and the Issuer shall not effect any such Triggering Event unless upon or
     prior to the consummation thereof the amounts of cash, property and/or
     Securities required under such clause (y) are delivered to the Holder of
     this Warrant.  The obligation of the Issuer to secure such right of the
     Holder to sell this Warrant shall be subject to such Holder's cooperation
     with the Issuer, including, without limitation, the giving of customary
     representations and warranties to the purchaser in connection with any such
     sale.  Prior notice of any Triggering Event shall be given to the Holder of
     this Warrant in accordance with Section 13 hereof.

     (b) Stock Dividends, Subdivisions and Combinations.  If at any time the
         ----------------------------------------------
Issuer shall:

         (i)  take a record of the holders of its Common Stock for the
     purpose of entitling them to receive a dividend payable in, or other
     distribution of, Additional Shares of Common Stock,

         (ii) subdivide its outstanding shares of Common Stock into a
     larger

                                      -6-
<PAGE>

     number of shares of Common Stock, or

               (iii) combine its outstanding shares of Common Stock into a
     smaller number of shares of Common Stock,

then (1) the number of shares of Common Stock for which this Warrant is
exercisable immediately after the occurrence of any such event shall be adjusted
to equal the number of shares of Common Stock which a record holder of the same
number of shares of Common Stock for which this Warrant is exercisable
immediately prior to the occurrence of such event would own or be entitled to
receive after the happening of such event, and (2) the Warrant Price then in
effect shall be adjusted to equal (A) the Warrant Price then in effect
multiplied by the number of shares of Common Stock for which this Warrant is
exercisable immediately prior to the adjustment divided by (B) the number of
shares of Common Stock for which this Warrant is exercisable immediately after
such adjustment.

     (c)  Certain Other Distributions.  If at any time the Issuer shall take a
          ---------------------------
record of the holders of its Common Stock for the purpose of entitling them to
receive any dividend or other distribution of:

               (i)   cash (other than a cash dividend payable out of earnings
     or earned surplus legally available for the payment of dividends under the
     laws of the jurisdiction of incorporation of the Issuer),

               (ii)  any evidences of its indebtedness, any shares of stock of
     any class or any other securities or property of any nature whatsoever
     (other than cash, Common Stock Equivalents or Additional Shares of Common
     Stock), or

               (iii) any warrants or other rights to subscribe for or purchase
     any evidences of its indebtedness, any shares of stock of any class or any
     other securities or property of any nature whatsoever (other than cash,
     Common Stock Equivalents or Additional Shares of Common Stock),

then (1) the number of shares of Common Stock for which this Warrant is
exercisable shall be adjusted to equal the product of the number of shares of
Common Stock for which this Warrant is exercisable immediately prior to such
adjustment multiplied by a fraction (A) the numerator of which shall be the Per
Share Market Value of Common Stock at the date of taking such record and (B) the
denominator of which shall be such Per Share Market Value minus the amount
allocable to one share of Common Stock of any such cash so distributable and of
the fair value (as determined in good faith by the Board of Directors of the
Issuer and supported by an opinion from an investment banking firm of recognized
national standing acceptable to the Holder) of any and all such evidences of
indebtedness, shares of stock, other securities or property or warrants or other
subscription or purchase rights so distributable, and (2) the Warrant Price then
in effect shall be adjusted to equal (A) the Warrant Price then in effect
multiplied by the number of shares of Common Stock for which this Warrant is
exercisable immediately prior to the adjustment divided by (B) the number of
shares of Common Stock for which this Warrant is exercisable immediately after
such adjustment.  A reclassification of the Common Stock (other

                                      -7-
<PAGE>

than a change in par value, or from par value to no par value or from no par
value to par value) into shares of Common Stock and shares of any other class of
stock shall be deemed a distribution by the Issuer to the holders of its Common
Stock of such shares of such other class of stock within the meaning of this
Section 4(c) and, if the outstanding shares of Common Stock shall be changed
into a larger or smaller number of shares of Common Stock as a part of such
reclassification, such change shall be deemed a subdivision or combination, as
the case may be, of the outstanding shares of Common Stock within the meaning of
Section 4(b).

     (d)  Issuance of Additional Shares of Common Stock.
          ---------------------------------------------

          (i)   In the event the Issuer, shall, at any time, from time to time,
issue or sell any shares of Common Stock (including Treasury Shares) to a third
party other than the Holder of this Warrant for a consideration per share less
than the Warrant Price then in effect for the Warrant immediately prior to the
time of such issue or sale, then, forthwith upon such issue or sale, the Warrant
Price then in effect for the Warrants shall be reduced to a price equal to the
consideration per share paid for such Common Stock and the number of shares of
Common Stock for which this Warrant is exercisable shall be increased by the
product of the number of shares of Common Stock for which this Warrant is
exercisable immediately prior to such issuance or sale multiplied by the
Dilution Percentage.  "Dilution Percentage" shall mean the percentage by which
the Warrant Price then in effect is reduced pursuant to this Section 4(d).

          (ii)  If at any time the Issuer shall at any time issue or sell any
Additional Shares of Common Stock to a third party other than the Holder of this
Warrant in exchange for consideration in an amount per Additional Share of
Common Stock less than the Per Share Market Value at the time the Additional
Shares of Common Stock are issued or sold, then, forthwith upon such issue or
sale, the Warrant Price then in effect for the Warrants shall be reduced by the
product of the Warrant Price then in effect multiplied by the Market Dilution
Percentage and the number of shares of Common Stock for which this Warrant is
exercisable shall be increased by the product of the number of shares of Common
Stock for which this Warrant is exercisable immediately prior to such issuance
or sale multiplied by the Market Dilution Percentage.  "Market Dilution
Percentage" shall mean the percentage by which such issuance or sale is below
the lesser of the Per Share Market Value or the per share market value of the
Common Stock as calculated pursuant to the terms of any other financings of the
Company.

          (iii) If at any time the Issuer shall issue or sell any Additional
Shares of Common Stock to a third party other than the Holder of this Warrant in
exchange for consideration in an amount per Additional Share of Common Stock
which is less than the Warrant Price or the Per Share Market Value at the time
the Additional Shares of Common Stock are issued or sold, the adjustment
required under Section 4(d) shall be made in accordance with the formula in
paragraph (i) or (ii) above which results in the lower Warrant Price following
such adjustment. The provisions of paragraphs (i) and (ii) of Section 4(d) shall
not apply to any issuance of Additional Shares of Common Stock for which an
adjustment is provided under Section 4(b) or 4(c). No adjustment of the number
of shares of Common Stock for which this Warrant shall be exercisable shall be
made under paragraph (i) or (ii) of Section 4(d) upon the issuance of any
Additional Shares of Common Stock which are issued pursuant to the exercise of

                                      -8-
<PAGE>

any warrants or other subscription or purchase rights or pursuant to the
exercise of any conversion or exchange rights in any Common Stock Equivalents,
if any such adjustment shall previously have been made upon the issuance of such
warrants or other rights or upon the issuance of such Common Stock Equivalents
(or upon the issuance of any warrant or other rights therefor) pursuant to
Section 4(e) or Section 4(f).

          (iv)  If the Issuer, at any time while this Warrant is outstanding,
shall issue any Additional Shares of Common Stock to the Holder of this Warrant
(otherwise than as provided in the foregoing subsections (a) through (c) of this
Section 4), at a price per share less than the Warrant Price then in effect or
without consideration, then the Warrant Price upon each such issuance shall be
adjusted to that price determined by multiplying the Warrant Price then in
effect by a fraction:

               (A) the numerator of which shall be equal to the sum of (x) the
          number of shares of Common Stock outstanding immediately prior to the
          issuance of such Additional Shares of Common Stock plus (y) the number
                                                             ----
          of shares of Common Stock which the aggregate consideration for the
          total number of such Additional Shares of Common Stock so issued would
          purchase at a price per share equal to the greater of the Per Share
          Market Value then in effect and the Warrant Price then in effect, and

               (B) the denominator of which shall be equal to the number of
          shares of Common Stock outstanding immediately after the issuance of
          such Additional Shares of Common Stock.


          (v)  The provisions of paragraph (iv) of Section 4(d) shall not apply
to any issuance of Additional Shares of Common Stock for which an adjustment is
provided under Section 4(a) through 4(c).  No adjustment of the number of shares
of Common Stock for which this Warrant shall be exercisable shall be made under
paragraph (iv) of Section 4(d) upon the issuance of any Additional Shares of
Common Stock which are issued pursuant to the exercise of any Common Stock
Equivalents, if any such adjustment shall previously have been made upon the
issuance of such Common Stock Equivalents (or upon the issuance of any warrant
or other rights therefor) pursuant to Section 4(e) or Section 4(f).

     (e)  Issuance of Warrants or Other Rights.  If at any time the Issuer shall
          ------------------------------------
take a record of the Holders of its Common Stock for the purpose of entitling
them to receive a distribution of, or shall in any manner (whether directly or
by assumption in a merger in which the Issuer is the surviving corporation)
issue or sell, any Common Stock Equivalents (or issue any warrant or other
rights therefor), whether or not the rights to exchange or convert thereunder
are immediately exercisable, and the price per share for which Common Stock is
issuable upon the exercise of such Common Stock Equivalents (or any warrant or
other rights therefor) shall be less than the Warrant Price in effect
immediately prior to the time of such issue or sale, then the number of shares
for which this Warrant is exercisable and the Warrant Price then in effect shall
be adjusted as provided in Section 4(d) on the basis that the maximum number of
Additional Shares of Common Stock issuable pursuant to all such Common Stock
Equivalents (or upon the issuance of any warrant or other rights therefor) shall
be deemed to have been issued and outstanding and the Issuer shall have received
all of the consideration payable therefor, if any, as

                                      -9-
<PAGE>

of the date of the actual issuance of such warrants or other rights. No
adjustments of the Warrant Price then in effect or the number of Warrant Shares
for which this Warrant is exercisable shall be made upon the actual issue of
such Common Stock or of such Common Stock Equivalents upon exercise of such
warrants or other rights or upon the actual issue of such Common Stock upon such
conversion or exchange of such Common Stock Equivalents.

     (f)  Issuance of Common Stock Equivalents.  If at any time the Issuer shall
          ------------------------------------
take a record of the Holders of its Common Stock for the purpose of entitling
them to receive a distribution of, or shall in any manner (whether directly or
by assumption in a merger in which the Issuer is the surviving corporation)
issue or sell, any Common Stock Equivalents, whether or not the rights to
exchange or convert thereunder are immediately exercisable, and the price per
share for which Common Stock is issuable upon such conversion or exchange shall
be less than the Warrant Price in effect immediately prior to the time of such
issue or sale, then the number of shares of Common Stock for which this Warrant
is exercisable and the Warrant Price then in effect shall be adjusted as
provided in Section 4(d) on the basis that the maximum number of Additional
Shares of Common Stock necessary to effect the conversion or exchange of all
such Common Stock Equivalents shall be deemed to have been issued and
outstanding and the Issuer shall have received all of the consideration payable
therefor, if any, as of the date of actual issuance of such Common Stock
Equivalents.  No further adjustment of the number of shares of Common Stock for
which this Warrant is exercisable and the Warrant Price then in effect shall be
made under this Section 4(f) upon the issuance of any Common Stock Equivalents
which are issued pursuant to the exercise of any warrants or other subscription
or purchase rights therefor, if any such adjustment shall previously have been
made upon the issuance of such warrants or other rights pursuant to Section
4(e).  No further adjustments of the number of shares of Common Stock for which
this Warrant is exercisable and the Warrant Price then in effect shall be made
upon the actual issue of such Common Stock upon conversion or exchange of such
Common Stock Equivalents.

     (g)  Superseding Adjustment.  If, at any time after any adjustment of the
          ----------------------
number of shares of Common Stock for which this Warrant is exercisable and the
Warrant Price then in effect shall have been made pursuant to Section 4(e) or
Section 4(f) as the result of any issuance of warrants, other rights or Common
Stock Equivalents, and (i) such warrants or other rights, or the right of
conversion or exchange in such other Common Stock Equivalents, shall expire, and
all or a portion of such warrants or other rights, or the right of conversion or
exchange with respect to all or a portion of such other Common Stock
Equivalents, as the case may be shall not have been exercised, or (ii) the
consideration per share for which shares of Common Stock are issuable pursuant
to such Common Stock Equivalents, shall be increased solely by virtue of
provisions therein contained for an automatic increase in such consideration per
share upon the occurrence of a specified date or event, then for each
outstanding Warrant such previous adjustment shall be rescinded and annulled and
the Additional Shares of Common Stock which were deemed to have been issued by
virtue of the computation made in connection with the adjustment so rescinded
and annulled shall no longer be deemed to have been issued by virtue of such
computation.  Upon the occurrence of an event set forth in this Section 4(g)
above, there shall be a recomputation made of the effect of such Common Stock
Equivalents on the basis of: (i) treating the number of Additional Shares of
Common Stock or other property, if any, theretofore actually issued or issuable
pursuant to the previous exercise of any such warrants or

                                      -10-
<PAGE>

other rights or any such right of conversion or exchange, as having been issued
on the date or dates of any such exercise and for the consideration actually
received and receivable therefor, and (ii) treating any such Common Stock
Equivalents which then remain outstanding as having been granted or issued
immediately after the time of such increase of the consideration per share for
which shares of Common Stock or other property are issuable under such Common
Stock Equivalents; whereupon a new adjustment of the number of shares of Common
Stock for which this Warrant is exercisable and the Warrant Price then in effect
shall be made, which new adjustment shall supersede the previous adjustment so
rescinded and annulled.

     (h)  Purchase of Common Stock by the Issuer.  If the Issuer at any time
          --------------------------------------
while this Warrant is outstanding shall, directly or indirectly through a
Subsidiary or otherwise, purchase, redeem or otherwise acquire any shares of
Common Stock at a price per share greater than the Per Share Market Value, then
the Warrant Price upon each such purchase, redemption or acquisition shall be
adjusted to that price determined by multiplying such Warrant Price by a
fraction (i) the numerator of which shall be the number of shares of Common
Stock outstanding immediately prior to such purchase, redemption or acquisition
minus the number of shares of Common Stock which the aggregate consideration for
the total number of such shares of Common Stock so purchased, redeemed or
acquired would purchase at the Per Share Market Value; and (ii) the denominator
of which shall be the number of shares of Common Stock outstanding immediately
after such purchase, redemption or acquisition.  For the purposes of this
subsection (h), the date as of which the Per Share Market Price shall be
computed shall be the earlier of (x) the date on which the Issuer shall enter
into a firm contract for the purchase, redemption or acquisition of such Common
Stock, or (y) the date of actual purchase, redemption or acquisition of such
Common Stock.  For the purposes of this subsection (h), a purchase, redemption
or acquisition of a Common Stock Equivalent shall be deemed to be a purchase of
the underlying Common Stock, and the computation herein required shall be made
on the basis of the full exercise, conversion or exchange of such Common Stock
Equivalent on the date as of which such computation is required hereby to be
made, whether or not such Common Stock Equivalent is actually exercisable,
convertible or exchangeable on such date.

     (i)  Registration Adjustment.  On the dates that are twelve (12) months and
          -----------------------
eighteen (18) months following the effective date of the registration statement
registering the Warrant Stock, the Warrant Price shall be adjusted to an amount
equal to 120% of the average of the Per Share Market Value for the five (5)
Trading Days having the lowest Per Share Market Value during the fifteen (15)
Trading Days immediately prior to such adjustment dates, provided that such
                                                         --------
adjusted price is lower than the Warrant Price.

     (j)  Other Provisions applicable to Adjustments under this Section.  The
          -------------------------------------------------------------
following provisions shall be applicable to the making of adjustments of the
number of shares of Common Stock for which this Warrant is exercisable and the
Warrant Price then in effect provided for in this Section 4:

          (i) Computation of Consideration.  To the extent that any Additional
              ----------------------------
Shares of Common Stock or any Common Stock Equivalents (or any warrants or other
rights therefor) shall be issued for cash consideration, the consideration
received by the Issuer therefor shall be the amount of the cash received by the
Issuer therefor, or, if such Additional Shares of Common

                                      -11-
<PAGE>

Stock or Common Stock Equivalents are offered by the Issuer for subscription,
the subscription price, or, if such Additional Shares of Common Stock or Common
Stock Equivalents are sold to underwriters or dealers for public offering
without a subscription offering, the initial public offering price (in any such
case subtracting any amounts paid or receivable for accrued interest or accrued
dividends and without taking into account any compensation, discounts or
expenses paid or incurred by the Issuer for and in the underwriting of, or
otherwise in connection with, the issuance thereof). To the extent that such
issuance shall be for a consideration other than cash, then, except as herein
otherwise expressly provided, the amount of such consideration shall be deemed
to be the fair value of such consideration at the time of such issuance as
determined in good faith by the Board of Directors of the Issuer. In case any
Additional Shares of Common Stock or any Common Stock Equivalents (or any
warrants or other rights therefor) shall be issued in connection with any merger
in which the Issuer issues any securities, the amount of consideration therefor
shall be deemed to be the fair value, as determined in good faith by the Board
of Directors of the Issuer, of such portion of the assets and business of the
nonsurviving corporation as such Board in good faith shall determine to be
attributable to such Additional Shares of Common Stock, Common Stock
Equivalents, or any warrants or other rights therefor, as the case may be. The
consideration for any Additional Shares of Common Stock issuable pursuant to any
warrants or other rights to subscribe for or purchase the same shall be the
consideration received by the Issuer for issuing such warrants or other rights
plus the additional consideration payable to the Issuer upon exercise of such
warrants or other rights. The consideration for any Additional Shares of Common
Stock issuable pursuant to the terms of any Common Stock Equivalents shall be
the consideration received by the Issuer for issuing warrants or other rights to
subscribe for or purchase such Common Stock Equivalents, plus the consideration
paid or payable to the Issuer in respect of the subscription for or purchase of
such Common Stock Equivalents, plus the additional consideration, if any,
payable to the Issuer upon the exercise of the right of conversion or exchange
in such Common Stock Equivalents. In case of the issuance at any time of any
Additional Shares of Common Stock or Common Stock Equivalents in payment or
satisfaction of any dividends upon any class of stock other than Common Stock,
the Issuer shall be deemed to have received for such Additional Shares of Common
Stock or Common Stock Equivalents a consideration equal to the amount of such
dividend so paid or satisfied.

          (ii)  When Adjustments to Be Made.  The adjustments required by this
                ---------------------------
Section 4 shall be made whenever and as often as any specified event requiring
an adjustment shall occur, except that any adjustment of the number of shares of
Common Stock for which this Warrant is exercisable that would otherwise be
required may be postponed (except in the case of a subdivision or combination of
shares of the Common Stock, as provided for in Section 4(b)) up to, but not
beyond the date of exercise if such adjustment either by itself or with other
adjustments not previously made adds or subtracts less than one percent (1%) of
the shares of Common Stock for which this Warrant is exercisable immediately
prior to the making of such adjustment.  Any adjustment representing a change of
less than such minimum amount (except as aforesaid) which is postponed shall be
carried forward and made as soon as such adjustment, together with other
adjustments required by this Section 4 and not previously made, would result in
a minimum adjustment or on the date of exercise. For the purpose of any
adjustment, any specified event shall be deemed to have occurred at the close of
business on the date of its occurrence.

                                      -12-
<PAGE>

          (iii) Fractional Interests.  In computing adjustments under this
                --------------------
Section 4, fractional interests in Common Stock shall be taken into account to
the nearest one one-hundredth (1/100/th/) of a share.

          (iv)  When Adjustment Not Required.  If the Issuer shall take a record
                ----------------------------
of the holders of its Common Stock for the purpose of entitling them to receive
a dividend or distribution or subscription or purchase rights and shall,
thereafter and before the distribution to stockholders thereof, legally abandon
its plan to pay or deliver such dividend, distribution, subscription or purchase
rights, then thereafter no adjustment shall be required by reason of the taking
of such record and any such adjustment previously made in respect thereof shall
be rescinded and annulled.  In addition, no adjustment shall be required under
Section 4(d)(i) hereof in the event the Issuer issues or sells Additional Shares
in a transaction whose primary purpose is to establish a relationship with the
recipient thereof for strategic reasons and not to raise capital.

     (k)  Form of Warrant after Adjustments.  The form of this Warrant need not
          ---------------------------------
be changed because of any adjustments in the Warrant Price or the number and
kind of Securities purchasable upon the exercise of this Warrant.

     (l)  Escrow of Warrant Stock.  If after any property becomes distributable
          -----------------------
pursuant to this Section 4 by reason of the taking of any record of the holders
of Common Stock, but prior to the occurrence of the event for which such record
is taken, and the Holder exercises this Warrant, any shares of Common Stock
issuable upon exercise by reason of such adjustment shall be deemed the last
shares of Common Stock for which this Warrant is exercised (notwithstanding any
other provision to the contrary herein) and such shares or other property shall
be held in escrow for the Holder by the Issuer to be issued to the Holder upon
and to the extent that the event actually takes place, upon payment of the
current Warrant Price.  Notwithstanding any other provision to the contrary
herein, if the event for which such record was taken fails to occur or is
rescinded, then such escrowed shares shall be cancelled by the Issuer and
escrowed property returned.

     5.   Notice of Adjustments.  Whenever the Warrant Price or Warrant Share
          ---------------------
Number shall be adjusted pursuant to Section 4 hereof (for purposes of this
Section 5, each an "adjustment"), the Issuer shall cause its Chief Financial
Officer to prepare and execute a certificate setting forth, in reasonable
detail, the event requiring the adjustment, the amount of the adjustment, the
method by which such adjustment was calculated (including a description of the
basis on which the Board made any determination hereunder), and the Warrant
Price and Warrant Share Number after giving effect to such adjustment, and shall
cause copies of such certificate to be delivered to the Holder of this Warrant
promptly after each adjustment.  Any dispute between the Issuer and the Holder
of this Warrant with respect to the matters set forth in such certificate may at
the option of the Holder of this Warrant be submitted to one of the national
accounting firms currently known as the "big five" selected by the Holder,
provided that the Issuer shall have ten (10) days after receipt of notice from
--------
such Holder of its selection of such firm to object thereto, in which case such
Holder shall select another such firm and the Issuer shall have no such right of
objection.  The firm selected by the Holder of this Warrant as provided in the
preceding sentence shall be instructed to deliver a written opinion as to such

                                      -13-
<PAGE>

matters to the Issuer and such Holder within thirty (30) days after submission
to it of such dispute.  Such opinion shall be final and binding on the parties
hereto.  The fees and expenses of such accounting firm shall be paid by the
Issuer.

     6.   Fractional Shares.  No fractional shares of Warrant Stock will be
          -----------------
issued in connection with and exercise hereof, but in lieu of such fractional
shares, the Issuer shall make a cash payment therefor equal in amount to the
product of the applicable fraction multiplied by the Per Share Market Value then
in effect.

     7.   Ownership Cap and Certain Exercise Restrictions.
          ------------------------------------------------

     (a)  Notwithstanding anything to the contrary set forth in this Warrant, at
no time may a holder of this Warrant exercise this Warrant if the number of
shares of Common Stock to be issued pursuant to such exercise would exceed, when
aggregated with all other shares of Common Stock owned by such holder at such
time, the number of shares of Common Stock which would result in such holder
owning more than 4.999% of all of the Common Stock outstanding at such time;
provided, however, that upon a holder of this Warrant providing the Issuer with
seventy-five (75) days notice (pursuant to Section 13 hereof) (the "Waiver
Notice") that such holder would like to waive this Section 7(a) with regard to
any or all shares of Common Stock issuable upon exercise of this Warrant, this
Section 7(a) will be of no force or effect with regard to all or a portion of
the Warrant referenced in the Waiver Notice.

     (b)  The Holder may not exercise the Warrant hereunder to the extent such
exercise would result in the Holder beneficially owning (as determined in
accordance with Section 13(d) of the Exchange Act and the rules thereunder) in
excess of 9.999% of the then issued and outstanding shares of Common Stock,
including shares issuable upon exercise of the Warrant held by the Holder after
application of this Section; provided, however, that upon a holder of this
Warrant providing the Issuer with the 75-day Waiver Notice that such holder
would like to waive this Section 7(b) with regard to any or all shares of Common
Stock issuable upon exercise of this Warrant, this Section 7(b) will be of no
force or effect with regard to all or a portion of the Warrant referenced in the
Waiver Notice.

     (c)  Notwithstanding anything to the contrary set forth herein, the Issuer
shall not be obligated to issue in excess of an aggregate of 6,578,000 shares of
Common Stock upon exercise of the Warrant and any shares of Common Stock
issuable in connection with the Purchase Agreement, which number of shares shall
be subject to adjustment pursuant to Section 4, and such number of shares, the
"Issuable Maximum".  The Issuable Maximum equals 19.999% of the number of shares
 ----------------
of Common Stock outstanding immediately prior to the Closing.  Shares of Common
Stock issued in respect of penalties and liquidated damages hereunder shall not
count towards the 6,578,000 share limit set forth in this paragraph and shall be
paid in cash as provided herein unless otherwise agreed to by the Holders.  If
on any Warrant exercise date (A) the Common Stock is listed for trading on
Nasdaq, (B) the Warrant Price then in effect is such that the aggregate number
of shares of Common Stock previously issued at a discount upon exercise of
Warrants or otherwise issued in connection with the Purchase Agreement, would
equal or exceed the Issuable Maximum, and (C) the Issuer shall not have
previously obtained the vote of shareholders (the "Shareholder Approval"), if
                                                   --------------------
any, as may be required by the applicable rules

                                      -14-
<PAGE>

and regulations of the Nasdaq Stock Market, Inc. (or any successor entity)
applicable to approve the issuance of share of Common Stock in excess of the
Issuable Maximum pursuant to the terms hereof, then the Issuer shall issue to
the holder so requesting such number of shares of Common Stock equal to the
Issuable Maximum and, with respect to the remainder of shares of Common Stock
which would result in an issuance of shares of Common Stock in excess of the
Issuable Maximum (the "Excess Shares"), the Issuer shall have the option to
                       -------------
either (1) use its reasonable efforts to obtain the Shareholder Approval
applicable to such issuance as soon as is possible, but in any event not later
than the 90/th/ day after such request, or (2) deliver to such holder cash in an
amount equal to the product of (x) the Per Share Market Value on the applicable
Warrant exercise date, and (y) the number of shares of Common Stock in excess of
such holder's pro rata portion of the Issuable Maximum that would have otherwise
been issuable to the holder but for the provisions of this Section (such amount
of cash being hereinafter referred to as the "Discount Equivalent"). If the
                                              -------------------
Issuer fails to pay the Discount Equivalent in full pursuant to this Section
within fifteen (15) days after the Issuer fails to obtain Shareholder Approval
pursuant to (1) above or the date payable pursuant to (2) above, the Issuer will
pay interest thereon at a rate of 10% per annum to the holder, accruing daily
from the applicable exercise until such amount, plus all such interest thereon,
is paid in full. The Issuer and the Holder understand and agree that shares of
Common Stock issued to and then held by the Holder as a result of exercise of
the Warrant or as a result of conversion of the Notes shall not be entitled to
cast votes on any resolution to obtain Shareholder Approval.

     8.   Intentionally Omitted.
          ---------------------

     9.   Definitions.  For the purposes of this Warrant, the following terms
          -----------
have the following meanings:

          "Additional Shares of Common Stock" means all shares of Common Stock
           ---------------------------------
     issued by the Issuer after the Original Issue Date, and all shares of Other
     Common, if any, issued by the Issuer after the Original Issue Date, except
     the Warrant Stock and shares of Common Stock issuable upon conversion of
     the Notes and except for:

               (A) Common Stock issued prior to the Original Issue Date to
     employees, consultants or directors of this corporation directly or
     pursuant to stock option plan(s) or restricted stock plan(s) approved by
     the Board of Directors of the Issuer;

               (B) the issuance of securities pursuant to the conversion or
     exercise of convertible or exercisable securities; or

               (C) Common Stock, issued, or issuable upon exercise of warrants,
     issued to vendors, financial institutions or lessors in connection with
     commercial credit arrangements, equipment financings or similar
     arrangements provided that such issuances are for primarily other than
     equity financing purposes and are approved by the Board of Directors of the
     Issuer.

          "Articles of Incorporation" means the Articles of Incorporation of the
           -------------------------
     Issuer as in effect on the Original Issue Date, and as hereafter from time
     to time amended, modified,

                                      -15-
<PAGE>

     supplemented or restated in accordance with the terms hereof and thereof
     and pursuant to applicable law.

          "Board" shall mean the Board of Directors of the Issuer.
           -----

          "Capital Stock" means and includes (i) any and all shares, interests,
           -------------
     participations or other equivalents of or interests in (however designated)
     corporate stock, including, without limitation, shares of preferred or
     preference stock, (ii) all partnership interests (whether general or
     limited) in any Person which is a partnership, (iii) all membership
     interests or limited liability company interests in any limited liability
     company, and (iv) all equity or ownership interests in any Person of any
     other type.

          "Common Stock" means the Common Stock, par value $.01 per share, of
           ------------
     the Issuer and any other Capital Stock into which such stock may hereafter
     be changed.

          "Common Stock Equivalent" means any Convertible Security or warrant,
           -----------------------
     option or other right to subscribe for or purchase any Additional Shares of
     Common Stock or any Convertible Security.

          "Convertible Securities" means evidences of Indebtedness, shares of
           ----------------------
     Capital Stock or other Securities which are or may be at any time
     convertible into or exchangeable for Additional Shares of Common Stock.
     The term "Convertible Security" means one of the Convertible Securities.

          "Governmental Authority" means any governmental, regulatory or self-
           ----------------------
     regulatory entity, department, body, official, authority, commission,
     board, agency or instrumentality, whether federal, state or local, and
     whether domestic or foreign.

          "Holders" mean the Persons who shall from time to time own any
           -------
     Warrant.  The term "Holder" means one of the Holders.

          "Independent Appraiser" means a nationally recognized or major
           ---------------------
     regional investment banking firm or firm of independent certified public
     accountants of recognized standing (which may be the firm that regularly
     examines the financial statements of the Issuer) that is regularly engaged
     in the business of appraising the Capital Stock or assets of corporations
     or other entities as going concerns, and which is not affiliated with
     either the Issuer or the Holder of any Warrant.

          "Issuer" means Vertel Corporation, a California corporation, and its
           ------
     successors.

          "Majority Holders" means at any time the Holders of Warrants
           ----------------
     exercisable for a majority of the shares of Warrant Stock issuable under
     the Warrants at the time outstanding.

          "Nasdaq" means The Nasdaq National Market.
           ------

                                      -16-
<PAGE>

          "Notes" means the convertible promissory notes issued in connection
           -----
     with the Purchase Agreement.

          "Original Issue Date" means August 31, 2001.
           -------------------

          "OTC Bulletin Board" means the over-the-counter electronic bulletin
           ------------------
     board.

          "Other Common" means any other Capital Stock of the Issuer of any
           ------------
     class which shall be authorized at any time after the date of this Warrant
     (other than Common Stock) and which shall have the right to participate in
     the distribution of earnings and assets of the Issuer without limitation as
     to amount.

          "Person" means an individual, corporation, limited liability company,
           ------
     partnership, joint stock company, trust, unincorporated organization, joint
     venture, Governmental Authority or other entity of whatever nature.

          "Per Share Market Value" means on any particular date (a) the closing
           ----------------------
     bid price per share of the Common Stock on such date on Nasdaq or another
     registered national stock exchange on which the Common Stock is then
     listed, or if there is no such price on such date, then the closing bid
     price on such exchange or quotation system on the date nearest preceding
     such date, or (b) if the Common Stock is not listed then on Nasdaq or any
     registered national stock exchange, the closing bid price for a share of
     Common Stock in the over-the-counter market, as reported by the OTC
     Bulletin Board or in the National Quotation Bureau Incorporated or similar
     organization or agency succeeding to its functions of reporting prices) at
     the close of business on such date, or (c) if the Common Stock is not then
     reported by the OTC Bulletin Board or the National Quotation Bureau
     Incorporated (or similar organization or agency succeeding to its functions
     of reporting prices), then the average of the "Pink Sheet" quotes for the
     relevant conversion period, as determined in good faith by the holder, or
     (d) if the Common Stock is not then publicly traded the fair market value
     of a share of Common Stock as determined by an Independent Appraiser
     selected in good faith by the Majority Holders; provided, however, that the
                                                     --------  -------
     Issuer, after receipt of the determination by such Independent Appraiser,
     shall have the right to select an additional Independent Appraiser, in
     which case, the fair market value shall be equal to the average of the
     determinations by each such Independent Appraiser; and provided, further
                                                            --------  -------
     that all determinations of the Per Share Market Value shall be
     appropriately adjusted for any stock dividends, stock splits or other
     similar transactions during such period.  The determination of fair market
     value by an Independent Appraiser shall be based upon the fair market value
     of the Issuer determined on a going concern basis as between a willing
     buyer and a willing seller and taking into account all relevant factors
     determinative of value, and shall be final and binding on all parties.  In
     determining the fair market value of any shares of Common Stock, no
     consideration shall be given to any restrictions on transfer of the Common
     Stock imposed by agreement or by federal or state securities laws, or to
     the existence or absence of, or any limitations on, voting rights.

                                      -17-
<PAGE>

          "Purchase Agreement" means the Note and Warrant Purchase Agreement
           ------------------
     dated as of August 31, 2001 among the Issuer and the investors a party
     thereto.

          "Securities" means any debt or equity securities of the Issuer,
           ----------
     whether now or hereafter authorized, any instrument convertible into or
     exchangeable for Securities or a Security, and any option, warrant or other
     right to purchase or acquire any Security.  "Security" means one of the
     Securities.

          "Securities Act" means the Securities Act of 1933, as amended, or any
           --------------
     similar federal statute then in effect.

          "Subsidiary" means any corporation at least 50% of whose outstanding
           ----------
     Voting Stock shall at the time be owned directly or indirectly by the
     Issuer or by one or more of its Subsidiaries, or by the Issuer and one or
     more of its Subsidiaries.

          "Term" has the meaning specified in Section 1 hereof.
           ----

          "Trading Day" means (a) a day on which the Common Stock is traded on
           -----------
     Nasdaq, or (b) if the Common Stock is not listed on Nasdaq, a day on which
     the Common Stock is traded on any other registered national stock exchange,
     or (c) if the Common Stock is not traded on any other registered national
     stock exchange, a day on which the Common Stock is traded on the OTC
     Bulletin Board, or (d) if the Common Stock is not traded on the OTC
     Bulletin Board, a day on which the Common Stock is quoted in the over-the-
     counter market as reported by the National Quotation Bureau Incorporated
     (or any similar organization or agency succeeding its functions of
     reporting prices); provided, however, that in the event that the Common
                        --------  -------
     Stock is not listed or quoted as set forth in (a), (b) and (c) hereof, then
     Trading Day shall mean any day except Saturday, Sunday and any day which
     shall be a legal holiday or a day on which banking institutions in the
     State of New York are authorized or required by law or other government
     action to close.

          "Voting Stock" means, as applied to the Capital Stock of any
           ------------
     corporation, Capital Stock of any class or classes (however designated)
     having ordinary voting power for the election of a majority of the members
     of the Board of Directors (or other governing body) of such corporation,
     other than Capital Stock having such power only by reason of the happening
     of a contingency.

          "Warrants" means the Warrants issued and sold pursuant to the Purchase
           --------
     Agreement, including, without limitation, this Warrant, and any other
     warrants of like tenor issued in substitution or exchange for any thereof
     pursuant to the provisions of Section 2(c), 2(d) or 2(e) hereof or of any
     of such other Warrants.

          "Warrant Price" means U.S. $.9988, as such price may be adjusted from
           -------------
     time to time as shall result from the adjustments specified in this
     Warrant, including Section 4 hereto.

                                      -18-
<PAGE>

          "Warrant Share Number" means at any time the aggregate number of
           --------------------
     shares of Warrant Stock which may at such time be purchased upon exercise
     of this Warrant, after giving effect to all prior adjustments and increases
     to such number made or required to be made under the terms hereof.

          "Warrant Stock" means Common Stock issuable upon exercise of any
           -------------
     Warrant or Warrants or otherwise issuable pursuant to any Warrant or
     Warrants.

     10.  Other Notices.  In case at any time:
          -------------

                    (A)  the Issuer shall make any distributions to the holders
                         of Common Stock; or

                    (B)  the Issuer shall authorize the granting to all holders
                         of its Common Stock of rights to subscribe for or
                         purchase any shares of Capital Stock of any class or of
                         any Common Stock Equivalents or other rights; or

                    (C)  there shall be any reclassification of the Capital
                         Stock of the Issuer; or

                    (D)  there shall be any capital reorganization by the
                         Issuer; or

                    (E)  there shall be any (i) consolidation or merger
                         involving the Issuer or (ii) sale, transfer or other
                         disposition of all or substantially all of the Issuer's
                         property, assets or business (except a merger or other
                         reorganization in which the Issuer shall be the
                         surviving corporation and its shares of Capital Stock
                         shall continue to be outstanding and unchanged and
                         except a consolidation, merger, sale, transfer or other
                         disposition involving a wholly-owned Subsidiary); or

                    (F)  there shall be a voluntary or involuntary dissolution,
                         liquidation or winding-up of the Issuer or any partial
                         liquidation of the Issuer or distribution to holders of
                         Common Stock;

then, in each of such cases, the Issuer shall give written notice to the Holder
of the date on which (i) the books of the Issuer shall close or a record shall
be taken for such dividend, distribution or subscription rights or (ii) such
reorganization, reclassification, consolidation, merger, disposition,
dissolution, liquidation or winding-up, as the case may be, shall take place.
Such notice also shall specify the date as of which the holders of Common Stock
of record shall participate in such dividend, distribution or subscription
rights, or shall be entitled to exchange their certificates for Common Stock for
securities or other property deliverable upon such reorganization,
reclassification, consolidation, merger, disposition, dissolution, liquidation
or winding-up, as the case may be.  Such notice shall be given at least ten (10)
days prior to the

                                      -19-
<PAGE>

action in question and not less than ten (10) days prior to the record date or
the date on which the Issuer's transfer books are closed in respect thereto. The
Issuer shall give to the Holder notice of all meetings and actions by written
consent of its stockholders, at the same time in the same manner as notice of
any meetings of stockholders is required to be given to stockholders who do not
waive such notice (or, if such requires no notice, then two (2) Trading Days
written notice thereof describing the matters upon which action is to be taken).
The Holder shall have the right to send two (2) representatives selected by it
to each meeting, who shall be permitted to attend, but not vote at, such meeting
and any adjournments thereof. This Warrant entitles the Holder to receive copies
of all financial and other information distributed or required to be distributed
to the holders of the Common Stock.

     11.  Amendment and Waiver.  Any term, covenant, agreement or condition in
          --------------------
this Warrant may be amended, or compliance therewith may be waived (either
generally or in a particular instance and either retroactively or
prospectively), by a written instrument or written instruments executed by the
Issuer and the Majority Holders; provided, however, that no such amendment or
                                 --------  -------
waiver shall reduce the Warrant Share Number, increase the Warrant Price,
shorten the period during which this Warrant may be exercised or modify any
provision of this Section 11 without the consent of the Holder of this Warrant.

     12.  Governing Law.  THIS WARRANT SHALL BE GOVERNED BY AND CONSTRUED IN
          -------------
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT GIVING EFFECT TO
PRINCIPLES OF CONFLICTS OF LAW.

     13.  Notices.  Any and all notices or other communications or deliveries
          -------
required or permitted to be provided hereunder shall be in writing and shall be
deemed given and effective on the earlier of (i) the date of transmission, if
such notice or communication is delivered via facsimile at the facsimile
telephone number specified for notice prior to 5:00 p.m., eastern time, on a
Trading Day, (ii) the Trading Day after the date of transmission, if such notice
or communication is delivered via facsimile at the facsimile telephone number
specified for notice later than 5:00 p.m., eastern time, on any date and earlier
than 11:59 p.m., eastern time, on such date, (iii) the Trading Day following the
date of mailing, if sent by nationally recognized overnight courier service or
(iv) actual receipt by the party to whom such notice is required to be given.
The addresses for such communications shall be with respect to the Holder of
this Warrant or of Warrant Stock issued pursuant hereto, addressed to such
Holder at its last known address or facsimile number appearing on the books of
the Issuer maintained for such purposes, or with respect to the Issuer,
addressed to:

                   Vertel Corporation
                   21300 Victory Boulevard
                   Suite 700
                   Woodland Hills, California 91367
                   Attention: Cyrus Irani, President and Chief Executive Officer
                   Telecopier: (818) 598-0104
                   Telephone:  (818) 227-1400

                                      -20-
<PAGE>

with copies (which copies shall not constitute notice to the Company) to:

                    Perkins Coie LLP
                    1620 26th Street, Sixth Floor
                    Santa Monica, CA 90404
                    Attention:  David J. Katz, Esq.
                    Telephone No.: (310) 788-3268
                    Facsimile No:  (310) 843-1254

Copies of notices to the Holder shall be sent to Jenkens & Gilchrist Parker
Chapin LLP, The Chrysler Building, 405 Lexington Avenue, New York, New York
10174, Attention: Christopher S. Auguste, Esq., facsimile no.: (212) 704-6288.
Any party hereto may from time to time change its address for notices by giving
at least ten (10) days written notice of such changed address to the other party
hereto.

     14.  Warrant Agent.  The Issuer may, by written notice to each Holder of
          -------------
this Warrant, appoint an agent having an office in New York, New York for the
purpose of issuing shares of Warrant Stock on the exercise of this Warrant
pursuant to subsection (b) of Section 2 hereof, exchanging this Warrant pursuant
to subsection (d) of Section 2 hereof or replacing this Warrant pursuant to
subsection (d) of Section 3 hereof, or any of the foregoing, and thereafter any
such issuance, exchange or replacement, as the case may be, shall be made at
such office by such agent.

     15.  Remedies.  The Issuer stipulates that the remedies at law of the
          --------
Holder of this Warrant in the event of any default or threatened default by the
Issuer in the performance of or compliance with any of the terms of this Warrant
are not and will not be adequate and that, to the fullest extent permitted by
law, such terms may be specifically enforced by a decree for the specific
performance of any agreement contained herein or by an injunction against a
violation of any of the terms hereof or otherwise.

     16.  Successors and Assigns.  This Warrant and the rights evidenced hereby
          ----------------------
shall inure to the benefit of and be binding upon the successors and assigns of
the Issuer, the Holder hereof and (to the extent provided herein) the Holders of
Warrant Stock issued pursuant hereto, and shall be enforceable by any such
Holder or Holder of Warrant Stock.

     17.  Modification and Severability.  If, in any action before any court or
          -----------------------------
agency legally empowered to enforce any provision contained herein, any
provision hereof is found to be unenforceable, then such provision shall be
deemed modified to the extent necessary to make it enforceable by such court or
agency.  If any such provision is not enforceable as set forth in the preceding
sentence, the unenforceability of such provision shall not affect the other
provisions of this Warrant, but this Warrant shall be construed as if such
unenforceable provision had never been contained herein.

                                      -21-
<PAGE>

     18.  Headings.  The headings of the Sections of this Warrant are for
          --------
convenience of reference only and shall not, for any purpose, be deemed a part
of this Warrant.

                                      -22-
<PAGE>

     IN WITNESS WHEREOF, the Issuer has executed this Warrant as of the day and
year first above written.


                            VERTEL CORPORATION



                            By: /s/ Craig Scott
                                -------------------------------
                                Name:  Craig Scott
                                Title: Vice President Finance & Admininstraion,
                                       Chief Financial Officer and Secretary

                                      -23-
<PAGE>

                                 EXERCISE FORM

                               VERTEL CORPORATION

The undersigned _______________, pursuant to the provisions of the within
Warrant, hereby elects to purchase _____ shares of Common Stock of Vertel
Corporation covered by the within Warrant.

Dated: _________________      Signature  ___________________________

                              Address    _____________________
                                         _____________________


                                   ASSIGNMENT

FOR VALUE RECEIVED, _________________ hereby sells, assigns and transfers unto
__________________ the within Warrant and all rights evidenced thereby and does
irrevocably constitute and appoint _____________, attorney, to transfer the said
Warrant on the books of the within named corporation.

Dated: _________________      Signature  ___________________________

                              Address    _____________________
                                         _____________________

                               PARTIAL ASSIGNMENT

FOR VALUE RECEIVED, _________________ hereby sells, assigns and transfers unto
__________________ the right to purchase _________ shares of Warrant Stock
evidenced by the within Warrant together with all rights therein, and does
irrevocably constitute and appoint ___________________, attorney, to transfer
that part of the said Warrant on the books of the within named corporation.

Dated: _________________      Signature  ___________________________

                              Address    _____________________
                                         _____________________

                          FOR USE BY THE ISSUER ONLY:

This Warrant No. W-_____ canceled (or transferred or exchanged) this _____ day
of ___________, _____, shares of Common Stock issued therefor in the name of
_______________, Warrant No. W-_____ issued for ____ shares of Common Stock in
the name of _______________.

                                      -24-