Document:

<PAGE>

                                                                     EXHIBIT 4.4

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933, AS AMENDED OR APPLICABLE STATE LAWS, AND MAY NOT BE
SOLD, PLEDGED, OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION
THEREOF UNDER SUCH LAWS PURSUANT TO RULE 144 OR AN OPINION OF COUNSEL REASONABLY
SATISFACTORY TO THE CORPORATION AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT
REQUIRED.

                           WARRANT TO PURCHASE STOCK

Corporation: Open Port Technology, Inc., an Illinois corporation
Number of Shares 150,000 (subject to the provisions set forth below)
Class of Stock: Series C Preferred
Initial Exercise Price: $2.025 per share
Issue Date: January 28, 1999
Expiration Date: The later of either (a) January 28, 2004 or (b) the second
anniversary of the Company's initial purchase offering.

     THIS WARRANT CERTIFIES THAT, for the agreed upon value of $1.00 and for
other good and valuable consideration, SILICON VALLEY BANK ("Holder") is
entitled to purchase the number of fully paid and nonassessable shares of the
class of securities (the "Shares") of the corporation (the "Company") at the
initial exercise price per Share (the "Warrant Price") all as set forth above
and as adjusted pursuant to Article 2 of this Warrant, subject to the provisions
and upon the terms and conditions set forth in this Warrant. For purposes of
determining the foregoing, Holder shall be entitled to purchase 50,000 Shares
upon the execution of this Warrant. Notwithstanding the foregoing, in the event
that the outstanding Bridge Loan Advances, as defined in the Second Amended and
Restated Loan and Security Agreement, dated August 17, 1998, by and between
Company and Holder (the "Loan Agreement"), exceed $2,000,000, Holder shall be
entitled to an additional 25,000 Shares; in the event that the Committed Bridge
is not paid in its entirety on or before the Bridge Loan Maturity Date, each as
defined in the Loan Agreement, Holder shall be entitled to an additional 25,000
Shares and; in the event that the Committed Bridge Loan is not paid in its
entirety prior to May 31, 1999, Holder shall be entitled to an additional 50,000
Shares (collectively, the "Additional Shares"). Notwithstanding the foregoing,
such grant of the Additional Shares shall not be construed in any way as Bank's
agreement to (i) waive an Event of Default under the Loan Agreement; (ii)
forbear from exercise its rights and remedies if an Event of Default occurs,
exits or continues under the Loan Agreement; or (iii) extend the Bridge Loan
Maturity Date.

ARTICLE 1.  EXERCISE.
            --------

            1.1.  Method of Exercise.  Holder may exercise this Warrant by
                  ------------------
delivering a duly executed Notice of Exercise in substantially the form attached
as Appendix 1 to the principal office of the Company. Unless Holder is
exercising the conversion right set forth in Section 1.2, Holder shall also
deliver to the Company a check for the aggregate Warrant Price for the Shares
being purchased.

                                      -1-
<PAGE>

            1.2.  Conversion Right.  In lieu of exercising this Warrant as
                  ----------------
specified in Section 1.1, Holder may from time to time convert this Warrant, in
whole or in part, into a number of Shares determined by dividing (a) the
aggregate fair market value of the Shares or other securities otherwise issuable
upon exercise of this Warrant minus the aggregate Warrant Price of such Shares
by (b) the fair market value of one Share. The fair value of the Shares shall be
determined pursuant to Section 1.4.

            1.3.  Intentionally Omitted.
                  ---------------------

            1.4.  Fair Market Value.  If the Shares are traded in a public
                  -----------------
market, the fair market value of the Shares shall be the closing price of the
Shares (or the closing price of the Company's stock into which the Shares are
convertible) reported for the business day immediately before Holder delivers
its Notice of Exercise to the Company. If the Shares are not traded in a public
market, the Board of Directors of the Company shall determine fair market value
in its reasonable good faith judgment. The foregoing notwithstanding, if Holder
advises the Board of Directors in writing that Holder disagrees with such
determination, then the Company and Holder shall promptly agree upon a reputable
investment banking firm to undertake such valuation. If the valuation of such
investment banking firm is greater than that determined by the Board of
Directors, then all fees and expenses of such investment banking firm shall be
paid by the Company. In all other circumstance, such fees and expenses shall be
paid by Holder.

            1.5.  Delivery of Certificate and New Warrant.  Promptly after
                  ---------------------------------------
Holder exercises or converts this Warrant, the Company shall deliver to Holder
certificates for the Shares acquired and, if this Warrant has not been fully
exercised or converted and has not expired, a new Warrant representing the
Shares not so acquired.

            1.6.  Replacement of Warrants.  On receipt of evidence reasonably
                  -----------------------
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and, in the case of loss, theft or destruction, on delivery of an
indemnity agreement reasonably satisfactory in form and amount to the Company
or, in the case of mutilation, on surrender and cancellation of this Warrant,
the Company at its expense shall execute and deliver, in lieu of this Warrant, a
new warrant of like tenor.

            1.7.  Repurchase on Sale, Merger, or Consolidation of the Company.
                  -----------------------------------------------------------

                  1.7.1.  "Acquisition".  For the purpose of this Warrant,
                           ------------
"Acquisition" means any sale, license, or other disposition of all or
substantially all of the assets of the Company, or any reorganization,
consolidation, or merger of the Company where the holders of the Company's
securities before the transaction beneficially own less than 50% of the
outstanding voting securities of the surviving entity after the transaction.

                  1.7.2.  Assumption of Warrant.  Upon the closing of any
                          ---------------------
Acquisition the successor entity shall assume the obligations of this Warrant,
and this Warrant shall be exercisable for the same securities, cash, and
property as would be payable for the Shares issuable upon exercise of the
unexercised portion of this Warrant as if such Shares were

                                      -2-
<PAGE>

outstanding on the record date for the Acquisition and subsequent closing. The
Warrant Price shall be adjusted accordingly.

                  1.7.3   Purchase Right. Notwithstanding the foregoing, at the
                          --------------
election of Holder, the Company shall purchase the unexercised portion of this
Warrant for cash upon the closing of any Acquisition for an amount equal to (a)
the fair market value of any consideration that would have been received by
Holder in consideration of the Shares had Holder exercised the unexercised
portion of this Warrant immediately before the record date for determining the
shareholders entitled to participate in the proceeds of the Acquisition, less
(b) the aggregate Warrant Price of the Shares, but in no event less than zero.

ARTICLE 2.  ADJUSTMENTS TO THE SHARES.
            -------------------------

            2.1.  Stock Dividends, Splits, Etc.  If the Company declares or pays
                  -----------------------
a dividend on its common stock (or the Shares if the Shares are securities other
than common stock) payable in common stock, or other securities, subdivides the
outstanding common stock into a greater amount of common stock, or, if the
Shares are securities other than common stock, subdivides the Shares in a
transaction that increases the amount of common stock into which the Shares are
convertible, then upon exercise of this Warrant, for each Share acquired, Holder
shall receive, without cost to Holder, the total number and kind of securities
to which Holder would have been entitled had Holder owned the Shares of record
as of the date the dividend or subdivision occurred.

            2.2.  Reclassification, Exchange or Substitution.  Upon any
                  ------------------------------------------
reclassification, exchange, substitution, or other event that results in a
change of the number and/or class of the securities issuable upon exercise or
conversion of this Warrant, Holder shall be entitled to receive, upon exercise
or conversion of this Warrant, the number and kind of securities and property
that Holder would have received for the Shares if this Warrant had been
exercised immediately before such reclassification, exchange, substitution, or
other event. Such an event shall include any automatic conversion of the
outstanding or issuable securities of the Company of the same class or series as
the Shares to common stock pursuant to the terms of the Company's Articles of
Incorporation upon the closing of a registered public offering of the Company's
common stock. The Company or its successor shall promptly issue to Holder a new
Warrant for such new securities or other property in return for Warrants that
are being replaced. The new Warrant shall provide for adjustments which shall be
as nearly equivalent as may be practicable to the adjustments provided for in
this Article 2 including, without limitation, adjustments to the Warrant Price
and to the number of securities or property issuable upon exercise of the new
Warrant. The provisions of this Section 2.2 shall similarly apply to successive
reclassifications, exchanges, substitutions, or other events.

            2.3.  Adjustments for Combinations, Etc.  If the outstanding Shares
                  ---------------------------------
are combined or consolidated, by reclassification or otherwise, into a lesser
number of shares, the Warrant Price shall be proportionately increased.

            2.4.  Adjustments for Diluting Issuances.  The Warrant Price and the
                  ----------------------------------
number of Shares issuable upon exercise of this Warrant or, if the Shares are
Preferred Stock, the number of shares of common stock issuable upon conversion
of the Shares, shall be subject to adjustment,

                                      -3-
<PAGE>

from time to time in the manner set forth on Exhibit A in the event of Diluting
Issuances (as defined on Exhibit A).

            2.5.  No Impairment.  The Company shall not, by amendment of its
                  -------------
Articles of Incorporation or through a reorganization, transfer of assets,
consolidation, merger, dissolution, issue, or sale of securities or any other
voluntary action, avoid or seek to avoid the observance or performance of any of
the terms to be observed or performed under this Warrant by the Company, but
shall at all times in good faith assist in carrying out of all the provisions of
this Article 2 and in taking all such action as may be necessary or appropriate
to protect Holder's rights under this Article against impairment. 'if the
Company takes any action affecting the Shares or its common stock other than as
described above that adversely affects Holder's rights under this Warrant, the
Warrant Price shall be adjusted downward and the number of Shares issuable upon
exercise of this Warrant shall be adjusted upward in such a manner that the
aggregate Warrant Price of this Warrant is unchanged.

            2.6.  Fractional Shares.  No fractional Shares shall be issuable
                  -----------------
upon exercise or conversion of the Warrant and the number of Shares to be issued
shall be rounded down to the nearest whole Share. If a fractional share interest
arises upon any exercise or conversion of the Warrant, the Company shall
eliminate such fractional share interest by paying Holder amount computed by
multiplying the fractional interest by the fair market value of a full Share as
determined under Section 1.4.

            2.7.  Certificate as to Adjustments.  Upon each adjustment of the
                  -----------------------------
Warrant Price, the Company at its expense shall promptly compute such
adjustment, and furnish Holder with a certificate of its Chief Financial Officer
setting forth such adjustment and the facts upon which such adjustment is based.
The Company shall, upon written request, furnish Holder a certificate setting
forth the Warrant Price in effect upon the date thereof and the series of
adjustments leading to such Warrant Price.

ARTICLE 3.  REPRESENTATIONS AND COVENANTS OF THE COMPANY.
            --------------------------------------------

            3.1.  Representations and Warranties.  The Company hereby represents
                  ------------------------------
and warrants to the Holder as follows:

                  (a)  The initial Warrant Price referenced on the first page of
this Warrant is not greater than the price per share at which the Shares were
last issued in an arms-length transaction in which at least $500,000 of the
Shares were sold.

                  (b)  All Shares which may be issued upon the exercise of the
purchase right represented by this Warrant, and all securities, if any, issuable
upon conversion of the Shares, shall, upon issuance, be duly authorized, validly
issued, fully paid and nonassessable, and free of any liens and encumbrances
except for restrictions on transfer provided for herein or under applicable
federal and state securities laws.

                  (c)  The capitalization table attached hereto is true and
correct.

            3.2.  Notice of Certain Events.  If the Company proposes at any time
                  ------------------------
(a) to declare any dividend or distribution upon its common stock, whether in
cash, property, stock, or

                                      -4-
<PAGE>

other securities and whether or not a regular cash dividend; (b) to offer for
subscription pro rata to the holders of any class or series of its stock any
additional shares of stock of any class or series or other rights; (c) to effect
any reclassification or recapitalization of common stock; (d) to merge or
consolidate with or into any other corporation, or sell, lease, license, or
convey all or substantially all of its assets, or to liquidate, dissolve or wind
up; or (e) offer holders of registration rights the opportunity to participate
in an underwritten public offering of the company's securities for cash, then,
in connection with each such event, the Company shall give Holder (1) at least
20 days prior written notice of the date on which a record will be taken for
such dividend, distribution, or subscription rights (and specifying the date on
which the holders of common stock will be entitled thereto) or for determining
rights to vote, if any, in respect of the matters referred to in (c) and (d)
above; (2) in the case of the matters referred to in (c) and (d) above at least
20 days prior written notice of the date when the same will take place (and
specifying the date on which the holders of common stock will be entitled to
exchange their common stock for securities or other property deliverable upon
the occurrence of such event); and (3) in the case of the matter referred to in
(e) above, the same notice as is given to the holders of such registration
rights. Holder is not entitled to vote and is not entitled to any rights as a
shareholder of the Company until the Warrant is exercised for Shares.

            3.3.  Information Rights.  So long as the Holder holds this Warrant
                  ------------------
and/or any of the Shares, the Company shall deliver to the Holder (a) promptly
after mailing, copies of all notices or other written communications to the
shareholders of the Company, (b) within one hundred twenty (120) days after the
end of each fiscal year of the Company, the annual audited financial statements
'of the Company certified by independent public accountants of recognized
standing and (c) such other financial statements required under and in
accordance with any loan documents between Holder and the Company (or if there
are no such requirements [or if the subject loan(s) no longer are outstanding]),
then within forty-five (45) days after the end of each of the first three
quarters of each fiscal year, the Company's quarterly, unaudited financial
statements. To the extent Holder already receives information noted herein
pursuant to the Loan Agreement, delivery of the foregoing under the Loan
Agreement is sufficient under this Warrant.

            3.4.  Registration Under Securities Act of 1933, as amended.  The
                  -----------------------------------------------------
Company agrees that the Shares or, if the Shares are convertible into common
stock of the Company, such common stock, shall be subject to the registration
rights set forth on Exhibit B, if attached.

ARTICLE 4.  MISCELLANEOUS.
            -------------

            4.1.  Term: Notice of Expiration.  This Warrant is exercisable, in
                  --------------------------
whole or in part, at any time and from time to time on or before the Expiration
Date set forth above. The Company shall give Holder written notice of Holder's
right to exercise this Warrant in the form attached as Appendix 2 not more than
90 days and not less than 30 days before the Expiration Date. If the notice is
not so given, the Expiration Date shall automatically be extended until 30 days
after the date the Company delivers the notice to Holder.

            4.2.  Legends.  This Warrant and the Shares (and the securities
                  -------
issuable, directly or indirectly, upon conversion of the Shares, if any) shall
be imprinted with a legend in substantially the following form:

                                      -5-
<PAGE>

                  THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT
                  OF 1933, AS AMENDED OR UNDER APPLICABLE STATE SECURITIES LAWS,
                  AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED WITHOUT
                  AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH LAWS PURSUANT TO
                  RULE 144 -OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO
                  THE CORPORATION AND ITS COUNSEL THAT SUCH REGISTRATION IS NOT
                  REQUIRED.

            4.3.  Compliance with Securities Laws on Transfer.  This Warrant and
                  -------------------------------------------
the Shares issuable upon exercise this Warrant (and the securities issuable,
directly or indirectly, upon conversion of the Shares, if any) may not be
transferred or assigned in whole or in part without compliance with applicable
federal and state securities laws by the transferor and the transferee
(including, without limitation, the delivery of investment representation
letters and legal opinions reasonably satisfactory to the Company, as reasonably
requested by the Company). The Company shall not require Holder to provide an
opinion of counsel if the transfer is to an affiliate of Holder or if there is
no material question as to the availability of current information as referenced
in Rule 144(c), Holder represents that it has complied with Rule 144(d) and (e)
in reasonable detail, the selling broker represents that it has complied with
Rule 144(f), and the Company is provided with a copy of Holder's notice of
proposed sale.

            4.4.  Transfer Procedure.  Subject to the provisions of Section 4.3
                  ------------------
Holder may transfer all or part of this Warrant or the Shares issuable upon
exercise of this Warrant (or the securities issuable, directly or indirectly,
upon conversion of the Shares, if any) at any time to Silicon Valley Bancshares
or The Silicon Valley Bank Foundation, or to any affiliate of Holder, or, to any
other transferree by giving the Company notice of the portion of the Warrant
being transferred setting forth the name, address and taxpayer identification
number of the transferee and surrendering this Warrant to the Company for
reissuance to the transferees) (and Holder if applicable). Unless the Company is
filing financial information with the SEC pursuant to the Securities Exchange
Act of 1934, the Company shall have the right to refuse to transfer any portion
of this Warrant to any person who directly competes with the Company.

            4.5.  Notices. All notices and other communications from the Company
                  -------
to the Holder, or vice versa, shall be deemed delivered and effective when given
personally or mailed by first-class registered or certified mail, postage
prepaid, at such address as may have been furnished to the Company or the
Holder, as the case may be, in writing by the Company or such holder from time
to time. All notices to be provided under this Warrant shall be send to the
following address:

                  Silicon Valley Bank
                  Attn: Treasury Department HG 250
                  3003 Tasman Drive
                  Santa Clara, CA 95054

                                      -6-
<PAGE>

            4.6.  Waiver.  This Warrant and any term hereof may be changed,
                  ------
waived, discharged or terminated only by an instrument in writing signed by the
party against which enforcement of such change, waiver, discharge or termination
is sought.

            4.7.  Attorneys Fees.  In the event of any dispute between the
                  --------------
parties concerning the terms and provisions of this Warrant, the party
prevailing in such dispute shall be entitled to collect from the other party all
costs incurred in such dispute, including reasonable attorneys' fees.

            4.8.  Governing Law.  This Warrant shall be governed by and
                  -------------
construed in accordance with the laws of the State of California, without giving
effect to its principles regarding conflicts of law.

                                     "COMPANY"

                                     OPEN PORT TECHNOLOGY, INC.

                                     By: /s/ Randy S. Storch
                                        ________________________________________

                                     Name: R. Storch
                                          ______________________________________
                                            (Print)
                                     Title: Chairman of the Board, President or
                                            Vice President

                                     By: /s/ David P. Aniol
                                        ________________________________________

                                     Name: D.P. Aniol
                                          ______________________________________
                                            (Print)
                                     Title: Chief Financial Officer, Secretary,
                                            Assistant Treasurer or Assistant
                                            Secretary

                                      -7-
<PAGE>

                                  APPENDIX 1

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

     1.  The undersigned hereby elects to purchase ____ shares of the
Common/preferred Series ___ [Strike one] Stock of sample pursuant to the terms
of the attached Warrant, and tenders herewith payment of the purchase price of
such shares in full.

     1.  The undersigned hereby elects to convert the attached Warrant into
Shares/cash [strike one] in the manner specified in the Warrant.  This
conversion is exercised with respect to of the Shares covered by the Warrant.

                    [Strike paragraph that does not apply.]

     2.  Please issue a certificate or certificates representing said shares in
the name of the undersigned or in such other name as is specified below:

                           ___________________________
                                    (Name)

                          ___________________________

                          ___________________________
                                   (Address)

     3.  The undersigned represents it is acquiring the shares solely for its
own account and not as a nominee for any other party and not with a view toward
the resale or distribution thereof except in compliance with applicable
securities laws.

                                                 ______________________________
                                                         (Signature)

 ______________________________
           (Date)

                                      -8-
<PAGE>

                                  APPENDIX 2

                    NOTICE THAT WARRANT IS ABOUT TO EXPIRE
                    --------------------------------------
                             ________________, ___

(Name of Holder)

(Address of Holder)

Attn:  Chief Financial Officer

Dear: _________________________

     This is to advise you that the Warrant issued to you described below will
expire on _________________, 19___.

               Issuer:
               Issue Date:
               Class of Security Issuable:
               Exercise Price per Share:
               Number of Shares Issuable:
               Procedure for Exercise:

     Please contact [name of contact person at (phone number)] with any
questions you may have concerning exercise of the Warrant. This is your only
notice of pending expiration.

                                             __________________________________
                                             (Name of Issuer)

                                             By:
                                             __________________________________
                                             Its:
                                             __________________________________

                                      -9-
<PAGE>

                                   EXHIBIT A
                                   ---------

                           Anti-Dilution Provisions
     (For Preferred Stock Warrants With Existing Anti-Dilution Protection)
     ---------------------------------------------------------------------

     In the event of the issuance (a "Diluting Issuance") by the Company, after
the Issue Date of the Warrant, of securities at a price per share less than the
Warrant Price, then the number of shares of common stock issuable upon
conversion of the Shares shall be adjusted in accordance with those provisions
(the "Provisions") of the Company's Articles (Certificate) of Incorporation
which apply to Diluting Issuances, including with respect to waivers or
amendments thereof, provided, that any amendment or waiver which adversely
affects Holder in a manner different than the other shareholders (other than
differences resulting solely from the class, series or number of Shares held by
Holder) may be effected only with the written consent of Holder.

     Under no circumstances shall the aggregate Warrant Price payable by the
Holder upon exercise of the Warrant increase as a result of any adjustment
arising from a Diluting Issuance.

                                      -10-
<PAGE>

                                   EXHIBIT B
                                   ---------

                              Registration Rights
                              -------------------

     The Shares (if common stock), or the common stock issuable upon conversion
of the Shares, shall be deemed "registrable securities" or otherwise entitled to
"piggy back" registration rights in accordance with the terms of the following
agreement (the "Agreement") between the Company and its investor(s):

               The Amended and Restated Registration Rights Agreement dated
               as of June 15, 1998, as amended, between Company and each
               Holder of its Preferred Stock.

     The Company agrees that no amendments will be made to the Agreement which
would have an adverse impact on Holder's registration rights thereunder without
the consent of Holder. Upon exercise of the Warrant to which this Exhibit B is
attached, Holder shall be deemed to be a party to the Agreement as a "Series C
Investor" thereunder, unless Holder otherwise elects not to become or to cease
being a party thereto.

     If no Agreement exists, then the Company and the Holder shall enter into
Holder's standard form of Registration Rights Agreement as in effect on the
Issue Date of the Warrant.

                                      -11-<PAGE>

                                                                     EXHIBIT 4.5

      Neither this warrant nor the shares of stock issuable upon exercise hereof
      have been registered under the Securities Act of 1933, as amended (the
      "Act") or under the laws of any state. No sale, transfer or other
      disposition of this warrant or such shares may be effected without (i) an
      effective registration statement under such laws related thereto or (ii)
      an opinion of counsel for the holder, or other evidence, reasonably
      satisfactory to the Company, that such registration is not required.

                          OPEN PORT TECHNOLOGY, INC.

                       PREFERRED STOCK PURCHASE WARRANT
                       --------------------------------

Date of Issuance:  June 22, 1998  Certificate No. PW-1

      FOR VALUE RECEIVED, OPEN PORT TECHNOLOGY, INC., an Illinois corporation
(the "Company"), hereby grants to Third Coast Venture Lease Partners I, L.P.
("Third Coast") or its registered assigns (the "Registered Holder") the right to
purchase from the Company 9,876 shares of Warrant Stock at a price per share of
$2.025 (as adjusted from time to time hereunder, the "Exercise Price").  This
Warrant is being issued pursuant to the terms of the Warrant Purchase Agreement,
dated as of June 22, 1998 (the "Purchase Agreement"), between the Company and
Third Coast.  Certain capitalized terms used herein are defined in Section 5
hereof.  The amount and kind of securities obtainable pursuant to the rights
granted hereunder and the purchase price for such securities are subject to
adjustment pursuant to the provisions contained in this Warrant.

      This Warrant is subject to the following provisions:

Section 1.  Exercise of Warrant.
            -------------------

1.A.   Exercise Period.  The Registered Holder may exercise, in whole or in
       ---------------
part, the purchase rights represented by this Warrant at any time and from time
to time after the date of issuance hereof to and including the tenth anniversary
of the Commencement Date (as defined in the Equipment Financing) of the last
Schedule under the Equipment Financing with Third Coast (the "Exercise Period").
The Company shall give the Registered Holder written notice of the expiration of
the Exercise Period at least 30 days but not more than 90 days prior to the end
of the Exercise Period.  For purposes
<PAGE>

of this Warrant, "Trigger Date" shall mean the date upon which the aggregate
amount of funds provided to the Company by Third Coast under the Equipment
Financing exceeds $500,000.

1.B.   Exercise Procedure.
       ------------------

(i)   This Warrant shall be deemed to have been exercised when the Company has
received all of the following items (the "Exercise Time"):

      (a)  a completed Exercise Agreement, as described in paragraph 1C below,
      executed by the Person exercising all or part of the purchase rights
      represented by this Warrant (the "Purchaser");

      (b)  this Warrant;

      (c)  if this Warrant is not registered in the name of the Purchaser, an
      Assignment or Assignments in the form set forth in Exhibit II hereto
                                                         ----------
      evidencing the assignment of this Warrant to the Purchaser, in which case
      the Registered Holder shall have complied with the provisions set forth in
      Section 7 hereof; and

      (d)  either (1) a cashier's check payable to the Company, or a wire
      transfer to the account designated by the Company, in an amount equal to
      the product of the Exercise Price multiplied by the number of shares of
      Warrant Stock being purchased upon such exercise (the "Aggregate Exercise
      Price"), (2) the surrender to the Company of debt or equity securities of
      the Company having a fair market value (determined by the Board of
      Directors in their reasonable good faith judgment) equal to the Aggregate
      Exercise Price of the Warrant Stock being purchased upon such exercise
      (provided that for purposes of this subparagraph, the fair market value of
      any note or other debt security or any preferred stock shall be deemed to
      be equal to the aggregate outstanding principal amount or liquidation
      value thereof plus all accrued and unpaid interest thereon or accrued or
      declared and unpaid dividends thereon) or (3) a written notice to the
      Company that the Purchaser is exercising the Warrant (or a portion
      thereof) by authorizing the Company to withhold from issuance a number of
      shares of Warrant Stock issuable upon such exercise of the Warrant which
      when multiplied by the Market Price of the Warrant Stock (assuming
      conversion thereof)is equal to the Aggregate Exercise Price (and such
      withheld shares shall no longer be issuable under this Warrant).

                                      -2-
<PAGE>

(ii) Certificates for shares of Warrant Stock purchased upon exercise of this
Warrant shall be delivered by the Company to the Purchaser within five business
days after the date of the Exercise Time. Unless this Warrant has expired or all
of the purchase rights represented hereby have been exercised, the Company shall
prepare a new Warrant, substantially identical hereto, representing the rights
formerly represented by this Warrant which have not expired or been exercised
and shall, within such five-day period, deliver such new Warrant to the Person
designated for delivery in the Exercise Agreement.

(iii) The Warrant Stock issuable upon the exercise of this Warrant shall be
deemed to have been issued to the Purchaser at the Exercise Time, and the
Purchaser shall be deemed for all purposes to have become the record holder of
such Warrant Stock at the Exercise Time.

(iv) The issuance of certificates for shares of Warrant Stock upon exercise of
this Warrant shall be made without charge to the Registered Holder or the
Purchaser for any issuance tax in respect thereof or other cost incurred by the
Company in connection with such exercise and the related issuance of shares of
Warrant Stock. Each share of Warrant Stock issuable upon exercise of this
Warrant shall, upon payment of the Exercise Price therefor, be fully paid and
nonassessable and free from all liens and charges with respect to the issuance
thereof, excluding taxes based on the income of Purchaser.

(v) Assuming the satisfaction of all conditions for transfer, the Company
shall not close its books against the transfer of this Warrant or of any share
of Warrant Stock issued or issuable upon the exercise of this Warrant in any
manner which interferes with the timely exercise of this Warrant. The Company
shall from time to time take all such action as may be necessary to assure that
the par value per share of the unissued Warrant Stock acquirable upon exercise
of this Warrant is at all times equal to or less than the Exercise Price then in
effect.

(vi) The Company shall reasonably cooperate with any Registered Holder or
Purchaser required to make any governmental filings or obtain any governmental
approvals prior to or in connection with any exercise of this Warrant
(including, without limitation, making any filings required to be made by the
Company), except for registrations under the Act, the Securities Exchange Act of
1934 or under the laws of any state.

(vii) Notwithstanding any other provision hereof, if an exercise of any portion
of this Warrant is to be made in connection with a registered public offering or
the sale of the Company, the

                                      -3-
<PAGE>

exercise of any portion of this Warrant may, at the election of the holder
hereof, be conditioned upon the consummation of the public offering or the sale
of the Company in which case such exercise shall not be deemed to be effective
until the consummation of such transaction.

(viii) The Company shall at all times reserve and keep available out of its
authorized but unissued shares of Warrant Stock solely for the purpose of
issuance upon the exercise of the Warrant, such number of shares of Warrant
Stock issuable upon the exercise of this Warrant. The Company shall take all
such actions as may be necessary to assure that all such shares of Warrant Stock
may be so issued without violation of any applicable law or governmental
regulation or any requirements of any domestic securities exchange upon which
shares of Warrant Stock may be listed (except for official notice of issuance
which shall be immediately delivered by the Company upon each such issuance).
The Company shall not take any action which would cause the number of authorized
but unissued shares of Warrant Stock to be less than the number of such shares
required to be reserved hereunder for issuance upon exercise of this Warrant.

1.C.      Exercise Agreement.  Upon any exercise of this Warrant, the Exercise
          ------------------
Agreement shall be substantially in the form set forth in Exhibit I hereto,
                                                          ---------
except that if the shares of Warrant Stock are not to be issued in the name of
the Person in whose name this Warrant is registered, the Exercise Agreement
shall also state the name of the Person to whom the certificates for the shares
of Warrant Stock are to be issued, and if the number of shares of Warrant Stock
to be issued does not include all the shares of Warrant Stock purchasable
hereunder, it shall also state the name of the Person to whom a new Warrant for
the unexercised portion of the rights hereunder is to be delivered. Such
Exercise Agreement shall be dated the actual date of execution thereof.

1.D.      Conversion or Redemption of the Preferred Stock.  Notwithstanding
          -----------------------------------------------
any other provision of this Warrant, if all of the issued and outstanding shares
of the Company's Preferred Stock are (i) converted automatically into shares of
Common Stock pursuant to paragraph 4(b) of the Company's Amended and Restated
Articles of Incorporation (the "Automatic Conversion") or (ii) redeemed by the
Company pursuant to paragraph 5 of the Company's Amended and Restated Articles
of Incorporation (the "Complete Redemption"), this Warrant shall no longer be
exercisable into shares of Preferred Stock but immediately upon the consummation
of the Automatic Conversion or the Complete Redemption shall become exercisable
into a number of shares of Common Stock equal to the number of shares of Common
Stock issuable upon conversion of the shares of Preferred Stock issuable upon
exercise of this Warrant as

                                      -4-
<PAGE>

of the consummation of such event at an Exercise Price equal to the Series C
Conversion Price (as defined under the Company's Amended and Restated Articles
of Incorporation) in effect as of the consummation of such event. Following the
occurrence of the Automatic Conversion or the Complete Redemption, the
provisions of this Warrant shall continue to apply to the Warrant Stock which
shall then be Common Stock. In addition to the foregoing, if the Complete
Redemption has occurred, within 90 days thereafter and prior to any exercise of
this Warrant, the holder of this Warrant may elect to surrender this Warrant to
the Company for an amount payable in cash upon such surrender equal to the
aggregate Fair Market Value (as defined in the Company's Amended and Restated
Articles of Incorporation) of the Preferred Stock issuable upon exercise of this
Warrant as of the Complete Redemption reduced by the aggregate Exercise Price of
this Warrant at such time.

Section 2.  Adjustment of Exercise Price and Number of Shares.  The Exercise
            -------------------------------------------------
Price and the number of shares of Warrant Stock issuable upon exercise of this
Warrant shall be subject to adjustment from time to time as provided in this
Section 2.

2.A.           Subdivision or Combination of Warrant Stock.  If the Company at
               -------------------------------------------
any time subdivides (by any stock split, stock dividend, recapitalization or
otherwise) the Warrant Stock into a greater number of shares, the Exercise Price
in effect immediately prior to such subdivision shall be proportionately reduced
and the number of shares of Warrant Stock obtainable upon exercise of this
Warrant shall be proportionately increased, and if the Company at any time
combines (by reverse stock split or otherwise) the Warrant Stock into a smaller
number of shares, the Exercise Price in effect immediately prior to such
combination shall be proportionately increased and the number of shares of
Warrant Stock obtainable upon exercise of this Warrant shall be proportionately
decreased.

2.B.           Reorganization, Reclassification, Consolidation, Merger or Sale.
               ---------------------------------------------------------------
Any recapitalization, reorganization, reclassification, consolidation, merger,
sale of all or substantially all of the Company's assets or other transaction,
which in each case is effected in such a way that the holders of Warrant Stock
are entitled to receive (either directly or upon subsequent liquidation) stock,
securities or assets with respect to or in exchange for Warrant Stock is
referred to herein as "Organic Change." Prior to the consummation of any Organic
Change, the Company shall make appropriate provision to insure that the
Registered Holder shall thereafter have the right to acquire and receive, in
lieu of or addition to (as the case may be) the shares of Warrant Stock
immediately theretofore acquirable and receivable upon the exercise of such
holder's Warrant, such shares of stock, securities or assets as may be issued or
payable with respect to or in exchange

                                      -5-
<PAGE>

for the number of shares of Warrant Stock immediately theretofore acquirable and
receivable upon exercise of such holder's Warrant had such Organic Change not
taken place. In any such case, the Company shall make appropriate provision with
respect to such holders' rights and interests to insure that the provisions of
this Section 2 and Sections 3 and 4 hereof shall thereafter be applicable to
this Warrant. The Company shall not effect any such consolidation, merger or
sale, unless prior to the consummation thereof, the successor entity (if other
than the Company) resulting from consolidation or merger or the entity
purchasing such assets assumes by written instrument, the obligation to deliver
to each such holder such shares of stock, securities or assets as, in accordance
with the foregoing provisions, such holder may be entitled to acquire.

2.C.           Certain Events.  If any event occurs of the type contemplated by
               --------------
the provisions of this Section 2 but not expressly provided for by such
provisions, then the Company's board of directors shall make an appropriate
adjustment in the Exercise Price and the number of shares of Warrant Stock
obtainable upon exercise of this Warrant so as to protect the rights of the
holder of this Warrant; provided that no such adjustment shall increase the
Exercise Price or decrease the number of shares of Warrant Stock obtainable as
otherwise determined pursuant to this Section 2.

2.D.           Adjustments.  No adjustments in the Exercise Price need be made
               -----------
if such adjustment would result in a change in the Exercise Price of less than
$0.01.  Any adjustment of less than $0.01 which is not made shall be carried
forward and shall be made at the time of and together with any subsequent
adjustment which, on a cumulative basis, amounts to an adjustment of $0.01 or
more in the Exercise Price.

2.E.           Notices.
               -------

(i) Immediately upon any adjustment of the Exercise Price, the Company shall
give written notice thereof to the Registered Holder, setting forth in
reasonable detail, and certifying the calculation of, such adjustment.

(ii) The Company shall give written notice to the Registered Holder at least 20
days prior to the date on which the Company closes its books or takes a record
(A) with respect to any dividend or distribution upon the Warrant Stock or the
Common Stock, (B) with respect to any pro rata subscription offer to holders of
Warrant Stock or Common Stock or (C) for determining rights to vote with respect
to any Organic Change, dissolution or liquidation.

                                      -6-
<PAGE>

(iii) The Company shall also give written notice to the Registered Holder at
least 20 days prior to the date on which any Organic Change, dissolution or
liquidation shall take place.

Section 3.  Definitions.  The following terms have meanings set forth below:
            -----------

             "Common Stock" means, collectively, the Company's Common Stock
              ------------
and any capital stock of any class of the Company hereafter authorized which is
not limited to a fixed sum or percentage of par or stated value in respect to
the rights of the holders thereof to participate in dividends or in the
distribution of assets upon any liquidation, dissolution or winding up of the
Company.

             "Equipment Financing" has the meaning set forth in the Purchase
              -------------------
Agreement.

             "Market Price" means with respect to each share of Common Stock:
              ------------

     (i) if the exercise is in connection with an initial public offering, and
     if the Company's Registration Statement relating to such public offering
     has been declared effective by the SEC, then the initial "Price to Public"
     specified in the final prospectus with respect to the offering (the
     foregoing shall not be construed as giving the Warrantholder any right to
     participate in or require any such initial public offering);

     (ii) if this Warrant is exercised after, and not in connection with the
     Company's initial public offering, and:

          (a)  if traded on a securities exchange, the Market Price shall be
               deemed to be the average of the closing prices over a twenty-one
               (21) day period ending three days before the day the current
               Market Price of the securities is being determined; or

          (b)  if actively traded over-the-counter, the Market Price shall be
               deemed to be the average of the closing bid and asked prices
               quoted on the NASDAQ system (or similar system) over the twenty-
               one (21) day period ending three days before the day the current
               Market Price of the securities is being determined ;

     (iii) if at any time the Common Stock is not listed on any securities
     exchange or quoted in the NASDAQ

                                      -7-
<PAGE>

     System or the over-the-counter market, the current Market Price of Common
     Stock shall be the highest price per share which the Company could obtain
     from a willing buyer (not a current employee or director) for shares of
     Common Stock sold by the Company, from authorized but unissued shares, as
     determined in good faith by its Board of Directors, unless the Company
     shall become subject to a merger, acquisition or other consolidation
     pursuant to which the Company is not the surviving party, in which case the
     Market Price of Common Stock shall be deemed to be the value received by
     the holders of the Company's Common Stock on a common equivalent basis
     pursuant to such merger or acquisition.

          "Person" means an individual, a partnership, a joint venture, a
           ------
corporation, a limited liability company, a trust, an unincorporated
organization and a government or any department or agency thereof.

          "Preferred Stock" means the Company's Series C Convertible
           ---------------
Participating Preferred Stock, par value $.001 per share.

          "Warrant Stock" means the Company's Preferred Stock; provided that if
           -------------
there is a change such that the securities issuable upon exercise of the Warrant
are issued by an entity other than the Company or there is a change in the type
or class of securities so issuable, then the term "Warrant Stock" shall mean one
share of the security issuable upon exercise of the Warrant if such security is
issuable in shares, or shall mean the smallest unit in which such security is
issuable if such security is not issuable in shares.

          Other capitalized terms used in this Warrant but not defined herein
shall have the meanings set forth in the Purchase Agreement.

Section 4.  No Voting Rights; Limitations of Liability.  This Warrant shall not
            ------------------------------------------
entitle the holder hereof to any voting rights or other rights as a stockholder
of the Company. No provision hereof, in the absence of affirmative action by the
Registered Holder to purchase Warrant Stock, and no enumeration herein of the
rights or privileges of the Registered Holder, shall give rise to any liability
of such holder for the Exercise Price of Warrant Stock acquirable by exercise
hereof or as a stockholder of the Company.

Section 5.  Warrant Transferable.  Subject to the transfer conditions referred
            --------------------
to in the legend endorsed hereon, this Warrant and all rights hereunder are
transferable, in whole or in

                                      -8-
<PAGE>

part, without charge to the Registered Holder, upon surrender of this Warrant
with a properly executed Assignment (in the form of Exhibit II hereto) at the
                                                    ----------
principal office of the Company.

Section 6.  Warrant Exchangeable for Different Denominations.  This Warrant is
            ------------------------------------------------
exchangeable, upon the surrender hereof by the Registered Holder at the
principal office of the Company, for new Warrants of like tenor representing in
the aggregate the purchase rights hereunder, and each of such new Warrants shall
represent such portion of such rights as is designated by the Registered Holder
at the time of such surrender. The date the Company initially issues this
Warrant shall be deemed to be the "Date of Issuance" hereof regardless of the
number of times new certificates representing the unexpired and unexercised
rights formerly represented by this Warrant shall be issued.

Section 7.  Replacement.  Upon receipt of evidence reasonably satisfactory to
            -----------
the Company (a sworn, notarized affidavit of the Registered Holder shall be
satisfactory) of the ownership and the loss, theft, destruction or mutilation of
any certificate evidencing this Warrant, and in the case of any such loss, theft
or destruction, upon receipt of indemnity reasonably satisfactory to the
Company, or, in the case of any such mutilation upon surrender of such
certificate, the Company shall (at the Warrantholder's expense) execute and
deliver in lieu of such certificate a new certificate of like kind representing
the same rights represented by such lost, stolen, destroyed or mutilated
certificate and dated the date of such lost, stolen, destroyed or mutilated
certificate.

Section 8.  Notices.  Except as otherwise expressly provided herein, all
            -------
notices referred to in this Warrant shall be in writing and shall be delivered
personally, sent by reputable overnight courier service (charges prepaid) or
sent by registered or certified mail, return receipt requested, postage prepaid
and shall be deemed to have been given when so delivered, sent or deposited in
the U. S. Mail (i) to the Company, at its principal executive offices and (ii)
to the Registered Holder of this Warrant, at such holder's address as it appears
in the records of the Company (unless otherwise indicated by any such holder).

Section 9.  Amendment and Waiver.  Except as otherwise provided herein, the
            --------------------
provisions of this Warrant may be amended and the Company may take any action
herein prohibited, or omit to perform any act herein required to be performed by
it, only if the Company has obtained the written consent of the Registered
Holder.

Section 10.  Descriptive Headings; Governing Law.  The descriptive headings of
             -----------------------------------
the several Sections and paragraphs of this

                                 *     *     *

                                      -9-
<PAGE>

Warrant are inserted for convenience only and do not constitute a part of this
Warrant. The corporation laws of the State of Illinois shall govern all issues
concerning the relative rights of the Company and its stockholders. All other
questions concerning the construction, validity, enforcement and interpretation
of this Warrant shall be governed by the internal law of the State of Illinois
without giving effect to any choice of law or conflict of law provision or rule
(whether of the State of Illinois or any other jurisdictions) that would cause
the application of the laws of any jurisdictions other than the State of
Illinois.

          IN WITNESS WHEREOF, the Company has caused this Warrant to be signed
and attested by its duly authorized officers under its corporate seal and to be
dated the Date of Issuance hereof.

                                OPEN PORT TECHNOLOGY, INC.

                                By:  ____________________________

                                Its: ___________________________

                                      -10-
<PAGE>

        SCHEDULE OF THIRD COAST VENTURE LEASE PARTNERS 1, L.P. WARRANTS

--------------------------------------------------------------------------------
                                                                Number of Shares
 No.           Date of Warrant          Exercise Price          Subject to
                                                                Purchase
--------------------------------------------------------------------------------
 1.            6/22/98                  $2.03                   9,876
--------------------------------------------------------------------------------
 2.            6/22/98                  $2.03                   9,877
--------------------------------------------------------------------------------

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