Document:

<PAGE>

                                                                   Exhibit 10.18

                           FIRST AMENDMENT TO LEASE
                           ------------------------

     This First Amendment to Lease (the "Agreement") is made and entered into as
of June 17, 1999 by and between SEAPORT CENTRE ASSOCIATES, LLC, a California
limited liability company ("Landlord") and PHONE.COM, INC., a Delaware
corporation, formerly know as Unwired Planet, Inc. ("Tenant").

                                   Recitals
                                   --------

     A.  Landlord and Tenant entered into a Lease dated March 10, 1998 (the
"Lease") by which Tenant leases from Landlord Building 15 containing
approximately 40,795 rentable square feet (the "Existing Premises") located at
800 Chesapeake Drive, Redwood City, California in a project known as Seaport
Centre Phase Three (West) (the "Project"). Capitalized terms not otherwise
defined in this Agreement shall have the meaning given them in the Lease.

     B.  The Tenn of the Lease is scheduled to expire on May 31, 2006 (the
"Expiration Date").

     C.  Tenant desires to lease additional space in the Project. Landlord and
Tenant desire to amend the Lease to provide foy Tenant to lease Building 16 (the
"Additional Building") containing approximately 24,600 rentable square feet
(the "Additional Space"), located at 600 Chesapeake Drive, Redwood City,
California, subject to the terms and conditions set forth in this Agreement. The
approximate configuration and location of the Additional Space is shown on
Exhibit A attached hereto.

     NOW THEREFORE, in consideration of the mutual promises contained herein,
and other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, the parties hereto agree as follows:

1.   Leasing of Additional Space. Commencing upon the date of this Agreement,
     Landlord hereby leases to Tenant and Tenant hereby leases from Landlord the
     Additional Space, subject to the different rent commencement dates for
     different portions of the Additional Space, as hereinafter provided. Tenant
     is considering occupying the Additional Space in phases (the "Phase 1
     Space") and (the "Phase 2 Space"). As of the date of this Agreement Tenant
     has not made a final decision as to whether Tenant will in fact occupy (x)
     different phases of the Additional Space at different times, or (y) the
     entire Additional Space at one time. From and after the date of this
     Agreement the parties agree that for all purposes under the Lease, the
     "Premises" shall contain approximately 65,395 rentable square feet.

2.   Term for Additional Space and Possession. If Tenant elects to occupy the
     Additional Space in phases, then the configuration and location of the
     Phase 1 and Phase 2 will

                                       1

<PAGE>

     be shown on the Construction Documents (as defined in the Construction
     Rider attached as Exhibit B attached hereto). Tenant's obligation to pay
     Base Rent and Additional Rent for the Phase 1 Space shall commence on the
     Phase 1 Rent Commencement Date (as hereinafter defined), and shall continue
     until the Expiration Date. Tenant's obligation to pay Base Rent and
     Additional Rent for the Phase 2 Space shall commence on the Phase
     2 Rent Commencement Date (as hereinafter defined), and shall continue until
     the Expiration Date. The "Phase 1 Rent Commencement Date" shall be the date
     on which Landlord tenders possession of the Phase 1 Space to Tenant with
     all of Landlord's construction obligations, if any, "Substantially
     Completed" in the Phase 1 Space, as provided in the Construction Rider
     attached as Exhibit B (the "Construction Rider") or, in the event of any
     "Tenant Delay," as defined in the Construction Rider, the date on which
     Landlord could have done so had there been no such Tenant Delay. The "Phase
     2 Rent Commencement Date" shall be the date on which Landlord tenders
     possession of the Phase 2 Space to Tenant with all of Landlord's
     construction obligations, if any, "Substantially Completed" in the Phase 2
     Space, as provided in the Construction Rider or, in the event of any
     "Tenant Delay" the date on which Landlord could have done so had there been
     no such Tenant Delay. The date Tenant anticipates occupying the Phase 1
     Space is on or about September 1, 1999 (the "Scheduled Phase 1 Rent
     Commencement Date"). The date Tenant anticipates occupying the Phase 2
     Space is on or about October 15, 1999 (the "Scheduled Phase 2 Rent
     Commencement Date"). Provided that Tenant delivers the Space Plan and the
     Final Construction Documents to Landlord within the times specified in the
     Construction Rider, Landlord agrees to use reasonable due diligence to
     deliver the Phase 1 Space and the Phase 2 Space to Tenant on the respective
     Scheduled Rent Commencement Dates; provided, however, that Landlord shall
     not be liable for any claims, damages or liabilities if the Phase 1 Space
     and the Phase 2 Space are not ready for occupancy by their respective
     Scheduled Rent Commencement Dates. When the Phase 1 Rent Commencement Date
     has been established, Landlord and Tenant shall at the request of either
     party confirm the Phase 1 Rent Commencement Date in writing. When the Phase
     2 Rent Commencement Date has been established, Landlord and Tenant shall at
     the request of either party confirm the Phase 2 Rent Commencement Date in
     writing.

3.   Existing Tenant. The Additional Space has been occupied by an existing
     tenant ("Existing Tenant") which was in holdover beyond the expiration of
     its lease. The Existing Tenant has vacated the Additional Space.

4.   Base Rent and Additional Rent for the Additional Space. In addition to the
     Base Rent payable by Tenant for the Existing Premises, Tenant shall pay
     Base Rent for the Additional Space in accordance with the provisions of the
     Lease and this Paragraph 4. Base Rent and Additional Rent for the Phase 1
     Space shall commence on the Phase 1 Rent Commencement Date and shall
     continue through the Expiration Date. Base Rent and Additional Rent for the
     Phase 2 Space shall commence on the Phase 2 Rent Commencement Date and
     shall continue through the Expiration Date. The following

                                       2

<PAGE>

     is the schedule of Base Rent for the Additional Space, which shall be
     payable by Tenant in accordance with the provisions of the Lease:

<TABLE>
<CAPTION>

       Months following, Phase 1                Monthly Base Rent per
       -------------------------                ---------------------
       Rent Commencement Date:                  Rentable Square Foot:
       -------------------------                ---------------------
      <S>                                       <C>
           Months 01 - 12:                               $2.45
           Months 13 - 24:                               $2.52
           Months 25 - 36:                               $2.60
           Months 37 - 48:                               $2.68
           Months 49 - 60:                               $2.76
           Months 61 - Expiration Date:                  $2.84
</TABLE>

5.   Tenant's Share. Tenant's Share with respect to the Phase 1 Space shall be
     appropriately adjusted on the Phase 1 Rent Commencement Date. Effective on
     the Phase 2 Rent Commencement Date, Tenant's Share is hereby changed to be
     48.35%.

6.   Building Systems in Additional Space. Prior to the Phase 1 Rent
     Commencement Date Landlord shall (a) deliver the roof of the Additional
     Building in good condition, and (b) cause the following systems
     (collectively, the "Building Systems") in the Additional Building to be
     inspected and placed in good working order and repair: (i) electrical, (ii)
     plumbing, and (iii) heating, ventilating and air-conditioning. If during
     the thirty (30) days following the Phase 1 Rent Commencement Date, any of
     the Building Systems in the Additional Building cease being in good working
     order and repair, and Tenant gives Landlord written notice of such failure
     within such thirty (30) days following the Phase 1 Rent Commencement Date,
     then Landlord shall cause such Building System to be placed in good working
     condition and repair, at no cost to Tenant. Except for any repairs and
     maintenance which are the responsibility of Landlord pursuant to the
     immediately preceding sentence, Tenant shall be responsible for all repairs
     and maintenance of the Building System in the Additional Building
     commencing on the thirty-first (31st) day following the Phase 1 Rent
     Commencement Date.

7.   Security Deposit. Upon execution of this Agreement Tenant shall deliver to
     Landlord a cash Security Deposit in the amount of $60,270.00 to be held by
     Landlord in accordance with the provisions of Section 4 of the Lease.

8.   Short Term Subleases. Notwithstanding any provision contained in Section
     14.7 of the Lease to the contrary, Tenant shall have the right, subject to
     the other provisions of Section 14 of the Lease, to sublease at any given
     time (whether through one or more subleases) up to, but not more than, a
     total of seventy-five percent (75%) of the entire Additional Space without
     Landlord having the right to terminate the Lease as it relates to the space
     proposed to be subleased by Tenant on the conditions that: (a) any such
     sublease must be entered into during the three (3) year period following
     the

                                       3
<PAGE>

     Phase 2 Rent Commencement Date, (b) the term of each such sublease shall
     not exceed three (3) years, and (c) the term of any such sublease shall
     expire on or before the date which is twelve (12) months prior to the
     Expiration Date.

9.   Letter of Credit. Reference is hereby made to Section 35 of the Lease.
     Within fifteen (15) days after the date (the "Market Value Deficiency
     Date"), if at all, during the Term, that Tenant's market capitalization
     (determined by multiplying the then current price of the publicly traded
     common stock as of any given date during the Term times the number of
     common shares outstanding) is less than $200,000,000.00, in addition to the
     L/C held by Landlord under Section 35 of the Lease, Tenant shall deliver to
     Landlord, a second L/C ("L/C #2") with a Face Amount equal to the "Amount
     Available Under the Letter of Credit" (as defined in the Lease) as of the
     Market Value Deficiency Date. If Tenant does not deliver L/C #2 to
     Landlord within fifteen (15) days after the Market Value Deficiency Date,
     and such failure continues for ten (10) days after written notice from
     Landlord to Tenant, then such failure shall constitute an Event of Default
     under the Lease. Landlord shall hold L/C #2 in accordance with the
     provisions of Section 35 of the Lease. Subject to the provisions and
     conditions of Section 35 (c) of the Lease, the amount available to be drawn
     under L/C #2 shall be equal to the amount available to be drawn under the
     L/C called for in Section 35 (c) of the Lease, as such amount may from
     time-to-time decrease.

10.  Environmental Claims with respect to Additional Space. The Existing Tenant
     has been occupying the Additional Space under permits (the "Environmental
     Permits") issued by governmental authorities which allow the Existing
     Tenant to use certain Hazardous Materials (the "Existing Tenant's Hazardous
     Materials") in the Additional Space. The Environmental Permits require the
     Existing Tenant to remove the Existing Tenant's Hazardous Materials from
     the Additional Space upon expiration or termination of the Existing
     Tenant's lease. The Existing Tenant has been in the process of removing
     such Existing Tenant's Hazardous Materials from the Additional Space in
     accordance with the Environmental Permits. Landlord shall be responsible,
     to the extent required by applicable Law, and without any cost to Tenant,
     to remove the Existing Tenant's Hazardous Materials from the Additional
     Space to the extent not Handled by Tenant.

11.  Monument Sign. Tenant shall have the right, at Tenant's sole cost and
     expense, to install a sign upon the existing monument which is located in
     front of the Building, subject to Landlord's reasonable approval, and
     subject to ordinances, regulations and any approval from the City of
     Redwood City.

12.  Broker. Landlord shall pay the fee or commission of the brokers, Cornish &
     Carey Commercial, and Wayne Mascia Associates (the "Brokers") in accordance
     with Landlord's separate written agreement with the Brokers, if any. Tenant
     warrants and represents to Landlord that in the negotiating or making of
     this Agreement neither Tenant nor anyone acting on Tenant's behalf has
     dealt with any broker or finder who might be entitled to a fee or
     commission for this Agreement other than the Brokers.

                                       4
<PAGE>

     Tenant shall indemnify and hold Landlord harmless from any claim or claims,
     including costs, expenses and attorney's fees incurred by Landlord asserted
     by any other broker or finder for a fee or commission based upon any
     dealings with or statements made by Tenant or Tenant's Representatives.

13.  Ratification of Lease. The Lease, as modified by this Agreement, remains in
     full force and effect, and Landlord and Tenant ratify the same. This
     Agreement shall be binding upon and inure to the benefit of the parties and
     their respective successors and assigns.

     If Tenant is a corporation or a partnership, each of the persons executing
this Agreement on behalf of Tenant warrants and represents that Tenant is a duly
authorized and existing entity that Tenant has full right and authority to enter
into this Agreement and that the persons signing on behalf of Tenant are
authorized to do so and have the power to bind Tenant to this Agreement. Tenant
shall provide Landlord, upon request, with evidence reasonably satisfactory to
Landlord confirming the foregoing representations.

     Except as herein amended, the Lease remains unchanged and is in full force
and effect in accordance with the terms and provisions contained therein.

     This First Amendment is hereby executed and delivered in multiple
counterparts, each of which shall have the force and effect of an original.

TENANT:                                LANDLORD:

PHONE.COM, INC.,                       SEAPORT CENTRE ASSOCIATES, LLC
(formerly know as Unwired              a California limited liability company
Planet, Inc.),
a Delaware corporation
                                       By: CORNERSTONE HOLDINGS, LLC,
                                           a Delaware limited liability company
                                           Manager

By: /s/ Alan Black                         By: /s/ illegible
    ---------------------------                ---------------------------------
Name: Alan Black                           Name: illegible
      -------------------------                  -------------------------------
Title: CFO                                 Title: Vice President
       ------------------------                   ------------------------------

By:
    ---------------------------
Name:
      -------------------------
Title:
       ------------------------

                                       5
<PAGE>

                                   EXHIBIT A
                                   ---------

                       ATTACHED TO AND FORMING A PART OF
                           FIRST AMENDMENT TO LEASE
                           DATED AS OF JUNE 17, 1999
                                    BETWEEN
                 SEAPORT CENTRE ASSOCIATES, LLC, AS LANDLORD,
                                      AND
                   PHONE.COM, INC., AS TENANT ("AGREEMENT")

                             THE ADDITIONAL SPACE
                             --------------------

                       600 Chesapeake Dr., Redwood City
                              Seaport Centre III

                           [PHOTO ADDITIONAL SPACE]

                               [PHOTO PROPERTY]

                                    [LOGOS]

                                                 INITIALS:

                                                 Landlord
                                                          ------------
                                                 Tenant.
                                                          ------------

                               Exhibit A, Page 1
<PAGE>

                                   EXHIBIT B
                                   ---------

                       ATTACHED TO AND FORMING A PART OF
                           FIRST AMENDMENT TO LEASE
                           DATED AS OF JUNE 17, 1999
                                    BETWEEN
                 SEAPORT CENTRE ASSOCIATES, LLC, AS LANDLORD,
                                      AND
                   PHONE.COM, INC., AS TENANT ("AGREEMENT")

                              CONSTRUCTION RIDER
                              ------------------

     1. Tenant Improvements. Landlord shall with reasonable diligence through
WCP Properties, Inc., dba Commercial Interior Contractors ("CIC") construct and
install in the Additional Space the improvements and fixtures provided for in
this Construction Rider ("Tenant Improvements"). Tenant acknowledges and agrees
that CIC is an affiliate of Landlord. CIC will complete the construction on an
open book basis and will competitively bid the major subcontracts (except for
those trades in which there will be design-build subcontracts). Upon request by
Landlord, Tenant shall designate in writing an individual authorized to act as
Tenant's Representative with respect to all approvals, directions and
authorizations pursuant to this Construction Rider.

          1.1. Plans. The Tenant Improvements shall be constructed substantially
as shown on the conceptual space plan ("Space Plan") for the Additional Space to
be prepared by the Space Planner who has been retained by Tenant as the space
planner for the Additional Space. The Space Planner shall be subject to
Landlord's prior approval, which approval shall not be unreasonably withheld.
Tenant shall cause the Space Planner to deliver the Space Plan to Landlord by
June 28, 1999 for Landlord's approval, which approval shall not be unreasonably
withheld. Landlord shall respond to the Space Plan within five (5) Business Days
after receipt thereof, specifying any changes or modifications Landlord
reasonably requires in the Space Plan. The Space Plan approved by Landlord is
the "Approved Space Plan."

          On or before July 28, 1999, Tenant will cause the Space Planner to
prepare and deliver to Landlord and Tenant detailed plans and specifications,
consistent with the Approved Space Plan, sufficient to permit CIC to construct
the Tenant Improvements ("Construction Documents"). Landlord will cause CIC to
provide Tenant with a cost estimate (the "First Cost Estimate") for the work
shown in the Construction Documents (the "First Construction Documents"). Tenant
shall respond to the First Construction Documents and First Cost Estimate within
three (3) Business Days after receipt thereof, specifying in detail any changes
or modifications Tenant desires in the First Construction Documents. Any changes
requested by Tenant to the First Construction Documents must be consistent with
the Approved Space Plan. The Space Planner will then revise the First
Construction Documents and resubmit them (the "Revised

                           Exhibit B, Page 1
<PAGE>

Construction Documents") to Landlord and Tenant for their approval and Landlord
will cause CIC to provide Tenant with a revised cost estimate (the "Revised Cost
Estimate"). Tenant shall approve the same within three (3) days after receipt.
The Revised Construction Documents and Revised Cost Estimate, as approved by
Tenant and Landlord, are hereinafter referred to as the "Final Construction
Documents" and "Final Cost Estimate," respectively.

     Additional interior decorating services and advice on the furnishing and
decoration of the Premises, such as the selection of fixtures, furnishings or
design of mill work, shall be provided by Tenant at its expense, but shall be
subject to the reasonable approval of Landlord.

          1.2. Construction. Upon approval by Landlord and Tenant of the Final
Construction Documents and the Final Cost Estimate, Landlord shall cause CIC to
proceed with reasonable diligence to Substantially Complete the Tenant
Improvements. The Tenant Improvements shall be deemed to be "Substantially
Complete" when they have been completed in accordance with the Final
Construction Documents except for finishing details, minor omissions,
decorations and mechanical adjustments of the type normally found on an
architectural "punch list". (The definition of Substantially Complete shall also
define the terms "Substantial Completion" and "Substantially Completed.")

     Following Substantial Completion of the Tenant Improvements and before
Tenant takes possession of the Additional Space (or as soon thereafter as may be
reasonably practicable and in any event within 30 days after Substantial
Completion), Landlord and Tenant shall inspect the Additional Space and jointly
prepare a "punch list" of agreed items of construction remaining to be
completed. Landlord shall complete the items set forth in the punch list as soon
as reasonably possible. Tenant shall cooperate with and accommodate Landlord and
Landlord's contractor in completing the items on the punch list.

          1.3. Cost of Tenant Improvements. Landlord shall contribute up to
$20.00 per rentable square foot in the Additional Space toward the cost of the
design (including preparation of space plans and Construction Documents),
construction and installation of the Tenant Improvements in the Additional
Space. The balance, if any, of the cost of the Tenant Improvements ("Additional
Cost"), including, but not limited to, usual markups for overhead, supervision
and profit, shall be paid by Tenant. Other than any construction fee payable to
CIC, Landlord shall not be entitled to any fee for supervision of the
construction of Tenant Improvements in the Additional Space. Tenant shall pay
CIC 50% of the Additional Cost based upon the Final Cost Estimate prior to the
commencement of construction of the Tenant Improvements. The balance of the
actual Additional Cost shall be paid by Tenant to CIC upon Substantial
Completion of the Tenant Improvements, within thirty (30) days after receipt of
Landlord's invoice therefor. Tenant's failure to pay the applicable portions of
the Additional Cost to CIC within three (3) Business Days after written demand
therefor shall constitute an Event of Default under the Lease. Landlord will use
reasonable care in causing CIC to prepare the cost estimates, but they are
estimates only and do not limit Tenant's obligation to pay for the actual
Additional Cost of the Tenant Improvements, whether or not it exceeds the
estimated amounts.

                            Exhibit B, Page 2
<PAGE>

          1.4. Changes. If Tenant requests any change, addition or alteration in
or to any Final Construction Documents ("Changes") Landlord shall cause the
Space Planner to prepare additional Plans implementing such Change. Tenant shall
pay the cost of preparing additional Plans. As soon as practicable after the
completion of such additional Construction Documents, Landlord shall notify
Tenant of the estimated cost of the Changes. Within three (3) working days after
receipt of such cost estimate, Tenant shall notify Landlord in writing whether
Tenant approves the Change. If Tenant approves the Change, Landlord shall
proceed with the Change and Tenant shall be liable for any Additional Cost
resulting from the Change. If Tenant fails to approve the Change within such
three (3) day period, construction of the Tenant Improvements shall proceed as
provided in accordance with the original Construction Documents.

          1.5. Delays. Tenant shall be responsible for, and shall pay to
Landlord, any and all costs and expenses incurred by Landlord in connection with
any delay in the commencement or completion of any Tenant Improvements and any
increase in the cost of Tenant Improvements caused by (i) Tenant's failure to
submit Space Plan or the First Construction Documents by the date specified
above, (ii) Tenant's making more than one (1) change to the Space Plan or First
Construction Documents, (iii) Tenant's failure to approve any cost estimates
within the time periods required herein, (iv) any delays in obtaining any items
or materials constituting part of the Tenant Improvements requested by Tenant,
(v) any Changes, or (vi) any other delay requested or caused by Tenant
(collectively, "Tenant Delays").

     2. Delivery of Additional Space. Upon Substantial Completion of the Tenant
Improvements, Landlord shall deliver possession of the Additional Space to
Tenant. If Landlord has not Substantially Completed the Tenant Improvements and
tendered possession of the Additional Space to Tenant on or before the Scheduled
Additional Space Commencement Date specified in the Agreement, or if Landlord is
unable for any other reason to deliver possession of the Additional Space to
Tenant on or before such date, neither Landlord nor its representatives shall be
liable to Tenant for any damage resulting from the delay in completing such
construction obligations and/or delivering possession to Tenant and this
Agreement shall remain in full force and effect unless and until it is
terminated under the express provisions of this Paragraph. If any delays in
Substantially Completing the Tenant Improvements are attributable to Tenant
Delays, then the Additional Space shall be deemed to have been Substantially
Completed and delivered to Tenant on the date on which Landlord could have
Substantially Completed the Additional Space and tendered the Additional Space
to Tenant but for such Tenant Delays.

     Notwithstanding the foregoing, if the Phase 2 Commencement Date has not
occurred or been deemed to have occurred within six (6) months after the
Scheduled Phase 2 Commencement Date, Tenant, by written notice to Landlord given
within ten (10) days after the expiration of such six (6) month period, may
terminate this Agreement without any liability to either party; provided,
however, that if the delay in the Phase 2 Commencement Date is caused by delays
of the type described in Section 26 - Force Majeure of the Lease, and if Tenant
elects to terminate as provided above, then Tenant shall reimburse Landlord,
within thirty (30) days after receipt of notification from Landlord of the
amounts due, for any amounts expended or incurred by Landlord for the design,
construction and installation of the Tenant Improvements and for brokerage
commissions

                            Exhibit B, Page 3
<PAGE>

and legal fees in connection with the preparation and negotiation of this
Agreement. If Tenant fails to perform any of Tenant's obligations under this
Construction Rider within the time periods specified herein, Landlord may, in
lieu of terminating this Agreement under the foregoing provisions, treat such
failure of performance as an Event of Default under the Lease.

     3. Access to Additional Space. Landlord shall allow Tenant and Tenant's
Representatives to enter the Additional Space prior to the Additional Space
Commencement Date to permit Tenant to make the Additional Space ready for its
use and occupancy; provided, however, that prior to such entry of the
Additional Space, Tenant shall provide evidence reasonably satisfactory to
Landlord that Tenant's insurance, as described in Section 11.1 - Tenant's
Insurance of the Lease, shall be in effect as of the time of such entry. Such
permission may be revoked at any time upon twenty-four (24) hours' notice, and
Tenant and its Representatives shall not interfere with Landlord or Landlord's
contractor in completing the Building or the Tenant Improvements.

     Tenant agrees that Landlord shall not be liable in any way for any injury,
loss or damage which may occur to any of Tenant's property placed upon or
installed in the Additional Space prior to the Additional Space Commencement
Date, the same being at Tenant's sole risk, and Tenant shall be liable for all
injury, loss or damage to persons or property arising as a result of such entry
into the Additional Space by Tenant or its Representatives.

     4. Ownership of Tenant Improvements. All Tenant Improvements, whether
installed by Landlord or Tenant, shall become a part of the Premises, shall be
the property of Landlord and, subject to the provisions of the Lease, shall be
surrendered by Tenant with the Premises, without any compensation to Tenant, at
the expiration or termination of the Lease in accordance with the provisions of
the Lease.

                                                         INITIALS:

                                                         Landlord
                                                                   ------
                                                         Tenant
                                                                   ------

                            Exhibit B, Page 4<PAGE>
                                                                   EXHIBIT 10.19

PERSONAL AND PRIVATE

October 4, 1999

Mr. Michael C. Mulica
2324 Lincolnwood Avenue
Evanston, IL 60201

Dear Mike:

I am delighted to confirm our offer to you to join Phone.com, Inc. Each person
at Phone.com, Inc. will help shape our values and direction, each person will
add his or her unique strengths and perspectives, and we are certainly looking
forward to your contributions to our growing company.

The offer is for you to join us as a Senior Vice President, Worldwide Sales,
Support and Consulting reporting to myself. Your monthly salary will be
$18,333.33 per month or $220,000 on an annualized basis, and your annual target
compensation will be $380,000, with the bonus based upon your performance in
achieving defined objectives in your position as Senior Vice President,
Worldwide Sales, Support and Consulting. For the first nine months of your
employment, you will receive a non-recoverable draw equal to your incentive
bonus. From that point on your incentives will be governed by the plan
provisions which include a 50% recoverable draw. As an employee you are also
eligible to receive our standard employee benefits.

Subject to the approval of the Board of Directors of Phone.com, Inc. you will be
granted an option to purchase.

1.  175,000 shares of Common Stock at an exercise price equal to the fair market
    value of the Common Stock at the date of grant. The shares will vest over
    four years with a one year cliff, meaning that one fourth of your shares
    will be vested one year from your hire date and the remaining shares will
    be vest monthly after your first year of employment for the following
    three years.

2.  25,000 shares of Common Stock at an exercise price equal to half of the
    closing price of the Common Stock on the date of grant. Vesting for this
    grant will commence on the date of grant and the shares will vest on a
    monthly basis over a period of four years. Note these options will be
    considered non-qualified stock options (NSO's) and will be subject to
    taxation at the time of exercise.

3.  Two blocks of 50,000 options which may be granted along with the first grant
    of 175,000 options or on the first day of the following two quarters,
    whichever you choose. However, you must make your performance on your date
    of hire. The shares will vest over four years with one year cliff, meaning
    that one fourth of your shares will be vested one year from your hire date
    and the remaining shares will vest monthly after your first year of
    employment for the following three years .

Vesting will of course, depend on your continued employment with Phone.com, Inc.
You will be offered to sign a "double trigger" agreement, which calls for
accelerated vesting of your stock if you are terminated with an 18 month period
after the Company is acquired.
<PAGE>
As we have discussed, we are extending additional financial support for your
relocation to the Bay Area. The relocation benefits available to you are
described below:

1.  Moving of typical and customary household goods to your primary residence in
    California, including two automobiles.

2.  Storage of household goods for up to 30 days.

3.  Reimbursement for real estate sales commissions on the sale of year existing
    residence in Evanston as well as your second home in Wisconsin up to maximum
    of $80,000 in total for both. It is expected that you will make every effort
    to minimize these costs through negotiated real estate sales commissions.

4.  Your may have the option to secure a one-time low-interest loan which will
    be secured against your primary California residence. The amount of this
    loan will be negotiated separately dependent on the specifics of your real
    estate transaction, with the interest and repayment terms of this loan being
    set forth in a separate loan agreement. It is understood that both you and
    Phone.com will be reasonable in the negotiation of this loan agreement.

5.  On the purpose of your primary residence in California, payment of closing
    costs that are typical for a buyer in the California area that are non-
    recurring and not negotiable or negotiated up to one percent (1%) of the
    purchase price.

6.  Temporary living accommodations for a period of up to 180 days at
    accommodations selected by Phone.com.

7.  Substitute transportation for a period of up to 30 days or until your
    personal vehicle arrives, whichever is sooner.

8.  Payment of expenses related to two house-hunting trips to the Bay Area with
    your spouse. This would include coach round trip airfare, rental care and
    per diem meal expenses.

9.  Use of local relocation counseling services as selected by the Company.

Any amounts received by you for relocation expenses will be reported as taxable
income to you in the year received as required by applicable tax law. Income
taxes which result from Company payments under this agreement are your
responsibility. You may wish to consult a tax advisor to clarify the tax
implications to you. Relocation must be completed and associated expenses must
be submitted to Phone.com, Inc. by not later than one year from your employment
date.

You should be aware that your employment with Phone.com, Inc. is for no
specified period and constitutes "at will" employment. As a result, you are
free to resign at any time, for any reason or for no reason. Similarly,
Phone.com is free to conclude its employment relationship with you at any time,
with or without cause. However, should your employment be terminated except "for
cause" during the first 24 months of employment, you will be eligible to receive
a severance package equal to 12 months of target pay and benefits, excluding the
further vesting of options. After 24 months of employment, this severance
package will be equal to six months of target pay and benefits again excluding
the further vesting of options.

[Cause" shall mean (i) gross negligence or willful misconduct in the performance
of the Employee's duties to the Company; (ii) repeated unexplained or
unjustified absence from the Company; (iii) a material and willful violation of
any federal or state law; (iv) refusal or failure to act in accordance with any
specific direction or order of the Company; (v) commission of any act of fraud
with respect to the Company; or (vi) conviction of a felony on a crime involving
moral turpitude causing material harm to the standing and reputation of the
Company, in each case as determined by the Board of Directors of the Company.]
<PAGE>

You are invited to attend Day One Orientation on your first day of work during
which you will learn more about UP's business, culture and benefits.
Orientation will be held from 9:00 AM to 11:00 AM in the Human Resources
Department. For purposes of Federal Immigration Law, you will be required to
provide to the Company documentary evidence of your identity and eligibility
for employment in the United States. Such documentation must be provided to us
within three (3) business days of your date of hire, or our employment
relationship with you may be terminated.

Upon joining Phone.com, Inc. you will be required to sign a confidentiality
and invention agreement in which you will be asked to protect the company's
confidential information and to assign to the company any inventions produced
in the course of your work.

This letter together with the confidentiality agreement sets forth the terms
of your employment with Phone.com, Inc. and supercedes any prior
representations or agreements, whether written or oral. This letter may not be
modified or amended except by a written agreement signed by Phone.com, Inc.
and you. Please review the terms to make sure they are consistent with your
understanding. If so, send back to me this signed offer letter no later than
Wednesday, October 6, 1999. As we have discussed, your expected start date is
on or before November 1, 1999.

Your acceptance of this offer represents a unique opportunity for Phone.com,
Inc. both to grow and to succeed. I want to thank you for the commitment you
have made to our common vision and look forward to working with you.

                                        Accepted by:

/s/ Alain Rossmann                      /s/ Michael Mulica
-------------------                     -------------------
Alain Rossmann                          Michael Mulica
Chairman and CEO

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