Document:

EXHIBIT 10.4

                             STOCK OPTION AGREEMENT

      THIS STOCK OPTION AGREEMENT (this "Agreement") is effective as of the 1st
day of May, 1999, by and between David Gergacz, an individual residing at 221
New Gate Loop, Heathrow, FL 32746 ("Gergacz"), and U.S. Mobile Services, Inc., a
Delaware corporation with its principal place of business at 7455-T New Ridge
Road, Hanover, MD 21076 ("USM").

                              W I T N E S S E T H:

      WHEREAS, Gergacz entered into an Employment Agreement dated May 1, 1999
with USM pursuant to which Gergacz is to be employed by USM as its Chairman and
Chief Executive Officer and which, among other provisions, specified the
issuance of this nonqualified stock option agreement,

      NOW, THEREFORE, and in consideration of the mutual covenants contained
herein, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, USM and Gergacz hereby agree as
follows:

            1. Grant of Option. Subject to the terms and conditions set forth
herein, USM hereby grants Gergacz the right and option (the "Option") to
purchase from USM the number of shares of USM Common Stock described in the
remainder of this paragraph (the "Shares") at the price of $.01 cash per share.
Initially, the Shares shall consist of 1,475,790 shares of USM Common Stock,
which number constitutes 15% of USM's total issued and outstanding Common Stock
as of the date of this Agreement. To the extent USM issues additional shares of
its Common Stock (or securities convertible into Common Stock), until such time
as USM has received a total of $6,000,000 of additional equity capital through
the sale of such Common Stock (or securities convertible into Common Stock), the
number of Shares subject to this Option shall be increased by an amount equal to
10% of the total number of shares of Common Stock issued (or issuable upon
conversion of other securities) in connection with USM's receipt of such
$6,000,000 of additional equity capital.

            2. Option Period; Vesting. The term of this Option shall commence on
the date first above written and expire on the earlier of at midnight on the
date that Gergacz's employment with USM terminates or at midnight on April 30,
2009 (the "Option Period"). This Option shall be immediately exercisable as to
one-third of the shares of USM Common Stock constituting the Shares. On November
1, 1999, the Option shall become exercisable as to an additional one-third of
the Shares. On May 1, 2000, the Option shall become exercisable as to the final
one-third of the Shares. The Option shall not be exercisable as to any Shares
after the expiration of the Option Period.

            3. Exercise of Option. Gergacz may exercise the Option from time to
time, in whole or in part (subject to the vesting provisions in Section 2
above), by giving USM written notice thereof, signed by Gergacz, prior to the
expiration of the Option Period. Upon USM's

<PAGE>

receipt of such a written notice of Gergacz's election to exercise the Option,
Gergacz shall pay USM the exercise price as specified in Section 1 hereof in
cash. Simultaneously with Gergacz's payment of the exercise price, USM will
issue the requisite number of Shares to Gergacz. Once Gergacz has exercised this
Option fully, this Agreement shall become null and void and Gergacz shall have
no further right to acquire any Shares of USM pursuant to this Agreement.

            4. Change of Control. In the event of a Change of Control as defined
below, this Option shall become immediately exercisable as to all Shares
notwithstanding the vesting schedule set forth above. For purposes of this
Agreement, the term "Change of Control" means any merger, consolidation, stock
purchase or any other transaction or series of related transactions involving
USM or any of its stockholders as a result of which any person or group of
persons (within the meaning of Section 13(d) of the Securities Exchange Act of
1934 and the rules promulgated thereunder) who are not as of the date hereof
stockholders of USM, come to possess at least a majority (in excess of 50%) of
the voting power of the outstanding capital stock of USM.

            5. Tax and Securities Laws. This Option is a nonqualified option for
tax purposes, which status involves various federal and state income tax
consequences which Gergacz understands and agrees to accept. The Shares, when
issued upon exercise of this Option, will constitute restricted securities
within the meaning of the Securities Act of 1933, and as such will be subject to
restrictions and limitations on transferability, with which Gergacz is familiar
and to which he agrees. The certificates representing such Shares will bear an
appropriate legend to such effect. USM shall file a registration statement
covering the Shares (so that they will not constitute restricted securities
following exercise of the Option) as soon as possible after the date USM becomes
a reporting company under the Securities Exchange Act of 1934 and is eligible to
use registration statement Form S-8. Gergacz hereby represents and warrants that
he is sophisticated as to financial matters and that he is an "accredited
investor" within the meaning of the rules promulgated under the Securities Act
of 1933.

            6. Binding Effect. This Agreement shall be binding upon and inure to
the benefit of the parties hereto, and their respective successors and assigns;
provided that Gergacz's rights and obligations hereunder may not be assigned
without prior written consent of USM.

            7. Notices. All notices provided for herein shall be deemed to have
been duly given if and when deposited in the United States mail with proper
first class postage affixed, properly addressed to the party for whom intended
and at the party's address as listed above or when personally delivered to such
party.

            8. Entire Agreement. It is expressly agreed by and between the
parties hereto as a material consideration for the execution of this Agreement
that there are and were no verbal or written representations, understandings,
stipulations, agreements or promises pertaining to the subject matter of this
Agreement not incorporated in writing herein. This Agreement nor any of the
provisions herein contained can be modified, terminated, superseded, waived or
extended except by an appropriate written instrument executed by the parties
hereto.

                                       2
<PAGE>

            9. Governing Law. This Agreement shall be governed by, and
interpreted in accordance with, the laws of the State of Maryland.

            10. Severability. Each Section of this Agreement shall be deemed
severable and if for any reason any Section or Subsection hereof is invalid or
contrary to any existing or future law, such invalidity shall not affect the
applicability or validity of any such other provision of this Agreement.

      IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the date first above written.

                                          /s/ David Gergacz
                                          --------------------------------------
                                          David Gergacz

                                          U.S. MOBILE SERVICES, INC.

                                          By: /s/ David Gergacz
                                             -----------------------------------

                                          Its:  Chief Executive Officer
                                              ----------------------------------

                                       3EXHIBIT 10.6

                            FORM OF LOCK-UP AGREEMENT

                                                        ____________ __, 2000

U.S. Mobile Services, Inc.
725 Primera Blvd., Suite 200
Lake Mary, Florida 32746

Ladies and Gentlemen:

      In order to induce certain investors to participate in a proposed private
placement (the "Offering") of shares of common stock, $0.001 par value per share
(the "Common Stock") of U.S. Mobile Services, Inc, a Delaware corporation (the
"Company"), the undersigned hereby agrees that, subject to the exception set
forth below, for a period of six (6) months from the closing of the Offering,
the undersigned will not directly or indirectly, issue, offer to sell, sell,
grant an option for the sale of, assign, transfer, pledge, hypothecate,
distribute or otherwise encumber or dispose of any shares of Common Stock or
securities convertible into, exercisable or exchangeable for or evidencing any
right to purchase or subscribe for any shares of Common Stock (either pursuant
to Rule 144 of the rules and regulations under the Securities Act of 1933, as
amended or otherwise) or dispose of any beneficial interest therein without the
prior written consent of the Company. The undersigned understands and
acknowledges that in connection with the above, the Company shall deliver
instructions to its transfer agent authorizing it to place appropriate stop
transfer orders on the Company's ledgers. Notwithstanding the above, it is
agreed that during each calendar month during the six month period, the
undersigned may sell an amount of Common Stock equal to 5% of the total amount
owned by the undersigned.

                                             Very truly yours,

                                             By: ______________________________
                                                 Name:EXHIBIT 10.27

                               2. AMENDMENT TO THE
               FRAMEWORK AGREEMENT AND SECURITY AGREEMENT (NOV 34)
                                     between
                        Novoste Corporation, Norcross GA
                                       and
             BEBIG Isotopentechnik und Umweltdiagnostik GmbH, Berlin

BACKGROUND

In a previous Amendment to the Framework Agreement and Security Agreement dated
23 July 1998 Novoste and BEBIG agreed to a number of procedures relating to the
return of source trains and the changing of the price formula. The provisions
have in part turned out to be unworkable. Both parties therefore agree to the
following modifications:

1.    Novoste may request from BEBIG, and BEBIG will accept, a final disposal of
      source trains for a flat disposal rate of XXXXX (XXXXX) per seed. BEBIG
      will send them to the "Zentralstelle fur Sammlung radioaktiver Abfalle
      (ZRA)", unless they were manufactured less than 12 months ago. In this
      case, BEBIG may recycle suitable seeds for further use.

2.    If trains for final disposal are received by BEBIG within 18 months from
      their date of manufacturing, as evidenced by the manufacturers
      certificate, then the charges for a second year use of the train (ss. 2,
      Amendment to the Framework Agreement and Security Agreement dated 23 July
      1998) will not apply.

3.    Novoste understands that BEBIG's ability to dispose off old source trains
      is contingent on various regulatory permissions. It explicitly grants
      BEBIG the right to cancel the disposal right or to increase the disposal
      charge if her disposal conditions change.

4.    In order to handle incoming trains and prepare them for disposal, BEBIG
      will need to develop a waste box, a number of tools, and the adequate
      handling processes. Since Novoste does not contribute to the investment,
      it will guarantee to BEBIG a disposal revenue per calendar year of at
      least XXXXX (XXXXX). In cases where the disposal volume is less then XXXXX
      per calendar year, Novoste will pay a the difference.

         Norcross, 2/11/00                                Berlin, 2/10/00
      ------------------------                       ------------------------
            Date/ Place                                     Date/ Place

      /s/ Novoste Corporation                        /s/ BEBIG GmbH
      ------------------------                       ------------------------

--------------------------------------------------------------------------------
Confidential treatment has been requested for portions of this page of this
exhibit. The copy filed herewith omits the information subject to the
confidentiality request. Omissions are designated as "XXXXX". The portions
omitted have been filed separately with the Securities and Exchange Commission
pursuant to such request for confidential treatment.

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00009-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00009-of-00352.parquet"}], [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00009-of-00352.parquet"}]]