<PAGE>   1
                                                                     EXHIBIT 4.2

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "1933 ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT
BE SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS IS
AVAILABLE WITH RESPECT THERETO.


              AMENDED AND RESTATED PREFERRED STOCK PURCHASE WARRANT




Warrant No. WBB-18                                    Number of Shares 14,205
                                                      Series BB Preferred Stock


                           REPEATER TECHNOLOGIES, INC.

                             Void after July 31, 2004



         1. ISSUANCE. This Amended and Restated Preferred Stock Purchase Warrant
replaces that certain Preferred Stock Purchase Warrant dated August 6, 1997
issued to LIGHTHOUSE CAPITAL PARTNERS II, LP. ("Lighthouse") by REPEATER
TECHNOLOGIES, INC., a California corporation (hereinafter with its successors
called the "Company").

         2. PURCHASE PRICE; NUMBER OF SHARES. The registered holder of this
Warrant (the "Holder"), commencing on the date hereof, is entitled upon
surrender of this Warrant with the subscription form annexed hereto duly
executed, at the principal of the Company, to purchase from the Company at a
price per share of $2.64 (the "Purchase Price"), 14,205 fully paid and
nonassessable shares (the "Shares") of Series BB Preferred Stock, no par value,
of the Company (the "Preferred Stock").

Until such time as this Warrant is exercised in full or expires, the Purchase
Price and the securities issuable upon exercise of this Warrant are subject to
adjustment as hereinafter provided. The person or persons on whose name or names
any certificate representing shares of Preferred Stock is issued hereunder shall
be deemed to have become the holder of record of the shares represented thereby
as at the close of business on the date this Warrant is exercised with respect
to such shares, whether or not the transfer books of the Company shall be
closed.

         3. PAYMENT OF PURCHASE PRICE. The Purchase Price may be paid (i) in
cash or by check, (ii) by the surrender by the Holder to the Company of any
promissory notes or other obligations issued by the Company, with all such
notes and obligations so surrendered being credited against the Purchase Price
in an amount equal to the principal amount thereof plus accrued interest to the
date of surrender, or (iii) by any combination of the foregoing.

         4. NET ISSUE ELECTION. The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares of Preferred Stock
equal to the value of this Warrant or any portion hereof by the surrender of
this Warrant or such portion to the Company, with the net issue election notice
annexed hereto duly executed, at the principal office of the Company. Thereupon,
the Company shall issue to the Holder such number of fully paid and
nonassesab1e shares of Preferred Stock as is computed using the following
formula:

                                    Y(A-B)
                                X = ------
                                      A



                                       1.
<PAGE>   2
where: X =        the number of shares of Preferred Stock to be issued to the
                  Holder pursuant to this Section 4.

                  Y =      the number of shares of Preferred Stock covered by
                           this Warrant in respect of which the net issue
                           election is made pursuant to this SECTION 4.

                  A =      the Fair Market Value (defined below) of one share
                           of Preferred Stock, as determined at the time the net
                           issue election is made pursuant to this SECTION 4.

                  B =      the Purchase Price in effect under this Warrant at
                           the time the net issue election is made pursuant to
                           this SECTION 4.

"Fair Market Value" of a share of Preferred Stock (or Common Stock if the
Preferred Stock has been automatically converted into Common Stock) as of a
particular date (the "Determination Date") shall mean:

                  (i) If the net issue election is made in connection with and
         contingent upon the closing of the sale of the Company's Common Stock
         to the public in a public offering pursuant to a Registration Statement
         under the Act (a "Public Offering"), and if the Company's Registration
         Statement relating to such Public Offering ("Registration Statement")
         has been declared effective by the SEC, then the initial "Price to
         Public" specified in the final prospectus with respect to such offering
         multiplied by the number of shares of Common Stock into which each
         share of Preferred Stock is then convertible.

                  (ii) If the net issue election is not made in connection with
         and contingent upon a Public Offering, then as follows:

                           (A) If traded on a securities exchange or the NASDAQ
                  National Market, the fair market value of the Common Stock
                  shall be deemed to be the average of the closing or last
                  reported sale prices of the Common Stock on such exchange or
                  market over the 30-day period ending five business days prior
                  to the Determination Date, and the fair market value of the
                  Preferred Stock shall be deemed to be such fair market value
                  of the Common Stock multiplied by the number of shares of
                  Common Stock into which each share of Preferred Stock is then
                  convertible;

                           (B) If otherwise traded in an over-the-counter
                  market, the fair market value of the Common Stock shall be
                  deemed to be the average of the closing ask prices of the
                  Common Stock over the 30-day period ending five business days
                  prior to the Determination Date, and the fair market value of
                  the Preferred Stock shall be deemed to be such fair market
                  value of the Common Stock multiplied by the number of shares
                  of Common Stock into which each share of Preferred Stock is
                  then convertible; and

                           (C) If there is no public market for the Common
                  Stock, then fair market value shall be determined by mutual
                  agreement of the holder of this Warrant and the Company, and
                  if the holder and the Company are unable to so agree, at the
                  Company's sole expense by an investment banker of national
                  reputation selected by the Company and reasonably acceptable
                  to the holder of this Warrant.

         5. PARTIAL EXERCISE. This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which this
Warrant shall not have been exercised.

         6. FRACTIONAL SHARE. In no event shall any fractional share of
Preferred Stock be issued upon any exercise of this Warrant. If, upon exercise
of this Warrant in its entirety, the Holder would, except as provided in this
SECTION 6, be entitled to receive a fractional share of Preferred Stock, then
the Company shall pay in lieu thereof, the Fair Market Value of such fractional
share in cash.



                                       2.
<PAGE>   3
         7. EXPIRATION DATE; AUTOMATIC EXERCISE. This Warrant shall expire at
the close of business on July 31, 2004 and shall be void thereafter.
Notwithstanding the foregoing, this Warrant shall automatically be deemed to be
exercised in full pursuant to the provisions of Section 4 hereof, without any
further action on behalf of the Holder, immediately prior to the time this
Warrant would otherwise expire pursuant to the preceding sentence.

         8. RESERVED SHARES; VALID ISSUANCE. The Company covenants that it will
at all times from and after the date hereof reserve and keep available such
number of its authorized shares of Preferred Stock and Common Stock, no par
value, of the Company (the "Common Stock"), free from all preemptive or similar
rights therein, as will be sufficient to permit, respectively, the exercise of
this Warrant in full and the conversion into shares of Common Stock of all
shares of Preferred Stock receivable upon such exercise. The Company further
covenants that such shares as may be issued pursuant to such exercise and/or
conversion will, upon issuance in accordance with the terms hereof, be duly and
validly issued, fully paid and nonassessable and free from all taxes, liens and
charges with respect to the issuance thereof.

         9. STOCK SPLITS AND DIVIDENDS. If after the date hereof the Company
shall subdivide the Preferred Stock, by split-up or otherwise, or combine the
Preferred Stock, or issue additional shares of Preferred Stock in payment of a
stock dividend on the Preferred Stock, the number of shares of Preferred Stock
issuable on the exercise of this Warrant shall forthwith be proportionately
increased in the case of a subdivision or stock dividend, or proportionately
decreased in the case of a combination, and the Purchase Price shall forthwith
be proportionately decreased in the case of a subdivision or stock dividend, or
proportionately increased in the case of a combination.

         10. REORGANIZATION, RECLASSIFICATIONS, CONSOLIDATION, MERGER OR SALE.
If any recapitalization, reclassification or reorganization of the capital stock
of the Company, or any consolidation or merger of the Company with another
corporation, or the sale of all or substantially all of its assets or other
transaction shall be effected in such a way that holders of the Preferred Stock
shall be entitled to receive stock, securities, or other assets or property (an
"Organic Change") then, as a condition of such Organic Change, lawful and
adequate provisions shall be made by the Company whereby the Holder hereof shall
thereafter have the right to purchase and receive (on the terms contained herein
and in lieu of the shares of the Preferred Stock of the Company immediately
theretofore purchasable and receivable upon the exercise of the rights
represented hereby) such shares of stock, securities or other assets or property
as may be issued or payable with respect to or in exchange for a number of
outstanding shares of such Preferred Stock equal to the number of shares of such
stock immediately theretofore purchasable and receivable upon the exercise of
the rights represented hereby, provided, however, that in the event the value of
the stock, securities or the assets or property (determined in good faith by the
Board of Directors of the Company) issuable or payable with respect to one share
of the preferred Stock of the Company immediately theretofore purchasable or
receivable upon the exercise of the rights represented hereby is in excess of an
amount equal to two times the Purchase Price hereof effective at the time of a
merger and securities received in such reorganization, if any, are publicly
traded, then this Warrant shall expire unless exercised prior to such Organic
Change. In the event of any Organic Change, appropriate provision shall be made
by the Company with respect to the provisions of this Warrant to the end that
such provisions (including, without limitation, provisions for adjustments of
the Purchase Price and the number of shares purchasable and receivable upon the
exercise of this Warrant) shall thereafter be applicable, in relation to any
shares of stock, securities or assets thereafter deliverable upon the exercise
hereof.

         11. CERTIFICATE OF ADJUSTMENT. Whenever the Purchase Price is adjusted,
as herein provided, the Company shall promptly deliver to the Holder a
certificate of the Company's chief financial officer setting forth the Purchase
Price after such adjustment and setting forth a brief statement of the facts
requiring such adjustment.

         12. NOTICES OF RECORD DATE, ETC. In the event of:

                  (a) any taking by the Company of a record of the holders of
any class of securities for the purpose of determining the holders thereof who
are entitled to receive any dividend or other distribution, or any


                                       3.
<PAGE>   4
right to subscribe for, purchase, sell or otherwise acquire or dispose of any
shares of stock of any class or any other securities or property, or to receive
any other right;

                  (b) any reclassification of the capital stock of the Company,
capital reorganization of the Company, consolidation or merger involving the
Company, or sale or conveyance of all or substantially all of its assets,
including any Organic Change; or

                  (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Company;

then in each such event the Company will provide or cause to be provided to the
Holder a written notice thereof. Such notice shall be provided at least ten (10)
business days prior to the date specified in such notice on which any such
action is to be taken.

         13. REPRESENTATIONS, WARRANTIES AND COVENANTS. This Warrant is issued
and delivered by the Company and accepted by each Holder on the basis of the
following representations, warranties and covenants made by the Company:

                  A. The Company has all necessary authority to issue, execute
and deliver this Warrant and to perform its obligations hereunder. This Warrant
has been duly authorized issued, executed and delivered by the Company and is
the valid and binding obligation of the Company, enforceable in accordance with
its terms.

                  B. The shares of Preferred Stock issuable upon the exercise of
this Warrant have been duly authorized and reserved for issuance by the Company
and, when issued in accordance with the terms hereof, will be validly issued,
fully paid and nonassessable.

                  C. The issuance, execution and delivery of this Warrant do
not, and the issuance of the shares of Preferred Stock upon the exercise of this
Warrant in accordance with the terms hereof will not, (i) violate or contravene
the Company's Articles or by-laws, or any law, statute, regulation, rule,
judgment or order applicable to the Company, (ii) violate, contravene or result
in a breach or default under any contract, agreement or instrument to which the
Company is a party or by which the Company or any of its assets are bound or
(iii) require the consent or approval of or the filing of any notice or
registration with any person or entity, except as may properly be made after the
date hereof.

                  D. Attached hereto as EXHIBIT D is a true and complete copy of
the Amended and Restated Articles of Incorporation of the Company in effect on
the date hereof.

                  E. So long as this Warrant has not terminated, Holder shall be
entitled to receive such financial and other information as the Holder would be
entitled to receive if Holder were a holder of more than 5% of any Registrable
Securities under the Fourth Amended and Restated Investor Rights Agreement,
dated September 3, 1996, as may be amended from time to time.

                  F. As of the date hereof, the authorized capital stock of the
Company consists of (i) 10,000,000 shares of Common Stock, of which 2,429,503
shares are issued and outstanding and 18,940 shares are reserved for issuance
upon the conversion of the Preferred Stock and exercise of this Warrant, (ii)
1,250,000 shares of Series AA Preferred Stock of which 1,228,409 are issued and
outstanding and (iii) 3,500,000 shares of Series BB Preferred Stock, of which
3,429,904 shares are issued and outstanding and 14,205 shares are reserved for
issuance upon the exercise of this Warrant. Attached hereto as EXHIBIT C is a
capitalization table summarizing the capitalization of the Company, including,
without limitation, the current Conversion Price of the Series BB Preferred
Stock.

         14. AMENDMENT. The terms of this Warrant may be amended, modified or
waived only with the written consent of the Holder and Company.



                                       4.
<PAGE>   5

         15. REPRESENTATIONS AND COVENANTS OF THE HOLDER. This Preferred Stock
Purchase Warrant has been entered into by the Company in reliance upon the
following representations and covenants of the Holder, which by its execution
hereof the Holder hereby confirms:

                  A. INVESTMENT PURPOSE. The right to acquire Preferred Stock or
the Preferred Stock issuable upon exercise of the Holder's rights contained
herein will be acquired for investment and not with a view to the sale or
distribution of any part thereof, and the Holder has no present intention of
selling or engaging in any public distribution of the same.

                  B. ACCREDITED INVESTOR. Holder is an "accredited investor"
within the meaning of the Securities and Exchange Rule 501 of Regulation D, as
presently in effect.

                  C. PRIVATE ISSUE. The Holder understands (i) that the
Preferred Stock issuable upon exercise of the Holder's rights contained herein
is not registered under the 1933 Act or qualified under applicable state
securities laws on the ground that the issuance contemplated by this Warrant
will be exempt from the registration and qualifications requirements thereof,
and (ii) that the Company's reliance on such exemption is predicated in part on
the representations set forth in this Section 15.

                  D. FINANCIAL RISK. The Holder has such knowledge and
experience in financial and business matters as to be capable of evaluating the
merits and risks of its investment and has the ability to bear the economic
risks of its investment.

         16. NOTICES, TRANSFERS, ETC.

                  A. Any notice or written communication required or permitted
to be given to the Holder may be given by certified mail or delivered to the
Holder at the address most recently provided by the Holder to the Company.

                  B. Subject to compliance with applicable federal and state
securities laws, this Warrant may only be transferred in its entirety by the
Holder with respect to all of the shares purchasable hereunder to any
affiliates of Lighthouse. Upon surrender of this Warrant to the Company,
together with the assignment notice annexed hereto duly executed, for transfer
of this Warrant as an entirety by the Holder, the Company shall issue a new
warrant of the same denomination to the assignee. Upon surrender of this Warrant
to the Company, together with the assignment hereof properly endorsed, by the
Holder for transfer with respect to a portion of the shares of Preferred Stock
purchasable hereunder, the Company shall issue a new warrant to the assignee, in
such denomination as shall be requested by the Holder hereof, and shall issue
to such Holder a new warrant covering the number of shares in respect of which
this Warrant shall not have been transferred.

                  C. In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and denomination
and deliver the same (i) in exchange and substitution for and upon surrender
and cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant lost,
stolen or destroyed, upon receipt of an affidavit of the Holder or other
evidence reasonably satisfactory to the Company of the loss, theft or
destruction of such Warrant and indemnification of the Company by the Holder
with respect thereto.

         17. NO IMPAIRMENT. The Company will not, by amendment of its Articles
or through any reclassification, capital reorganization, consolidation, merger,
sale or conveyance of assets, dissolution, liquidation, issue or sale of
securities or any other voluntary action, avoid or seek to avoid the observance
of performance of any of the terms of this Warrant, but will at all times in
good faith assist in the carrying out of all such terms and in the taking of all
such action as may be necessary or appropriate in order to protect the rights of
the Holder.

         18. GOVERNING LAW. The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State of
California.



                                       5.
<PAGE>   6

         19. SUCCESSORS AND ASSIGNS. This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the Holder's
successors, legal representatives and permitted assigns.

         20. BUSINESS DAYS. If the last or appointed day for the taking of any
action required or the expiration of any rights granted herein shall be a
Saturday or Sunday or a legal holiday in California, then such action may be
taken or right may be exercised on the next succeeding day which is not a
Saturday or Sunday or such a legal holiday.

         21. QUALIFYING PUBLIC OFFERING. If the Company shall effect a firm
commitment underwritten public offering of shares of Common Stock which results
in the conversion of the Preferred Stock into Common Stock pursuant to the
Company's Articles in effect immediately prior to such offering, then,
effective upon such conversion, this Warrant shall change from the right to
purchase shares of Preferred Stock to the right to purchase shares of Common
Stock, and the Holder shall thereupon have the right to purchased, at a total
price equal to that payable upon the exercise of this Warrant in full, the
number of shares of Common Stock which would have been receivable by the Holder
upon the exercise of this Warrant for shares of Preferred Stock immediately
prior to such conversion of such shares of Preferred Stock into shares of Common
Stock, and in such event appropriate provisions shall be made with respect to
the rights and interest of the Holder to the end that the provisions hereof
(including, without limitation, the provisions for the adjustment of the
Purchase Price and of the number of shares purchasable upon exercise of this
Warrant and the provisions relating to the net issue election) shall thereafter
be applicable to any shares of Common Stock deliverable upon the exercise
hereof.

         22. VALUE. The Company and the Holder agree that the value of this
Warrant on the date of grant is $100.

         23. RIGHTS OF THE HOLDER. The Holder shall not, by virtue hereof, be
entitled to any rights of a shareholder in the Company, either at law or
equity, and the rights of the Holder are limited to those expressed in this
Warrant. Nothing contained in this Warrant shall be construed as conferring upon
the Holder hereof the right to vote or to consent or to receive notice as a
shareholder of the Company on any matters or with respect to any rights
whatsoever as a shareholder of the Company. No dividends or interest shall be
payable or accrued in respect of this Warrant or the interest represented hereby
or the Shares purchasable hereunder until, and only to the extent that, this
Warrant shall have been exercised in accordance with its terms.

         24. MARKET STANDOFF. The holder of this Warrant, by acceptance hereof,
agrees (but only if each Company officer, director, and shareholder owning
beneficially 5% or more of the Company's equity securities, and each shareholder
selling shares in such offering, also agrees) that such holder will not,
without the prior written consent of the lead underwriter of the initial public
offering of the Common Stock of the Company pursuant to a registration statement
filed under the Act (the "Offering"), directly or indirectly offer to sell,
contact to sell (including, without limitation, any short sale), grant any
option for the sale of, acquire any option to dispose of any Warrant Shares for
a period of 180 days following the day on which the registration statement filed
on behalf of the Company in connection with the Offering shall become effective
by order of the SEC.

         25. DESCRIPTIVE HEADINGS. The description headings of the several
sections and paragraphs of this Warrant are inserted for convenience only and do
not constitute a part of this Warrant.



                                       6.
<PAGE>   7

         26. ENTIRE AGREEMENT. This Warrant and the attachments hereto
constitute the entire agreement between the parties pertaining to the subject
matter herein and supersedes all prior and contemporaneous agreements,
representations and undertakings of the parties.


                                             REPEATER TECHNOLOGIES, INC.


[CORPORATE SEAL]
                                             By: /s/ TODD B. SCHULL
                                                 --------------------------
                                             Name: Todd B. Schull
                                                   ------------------------
                                             Title: Vice President and CFO
                                                    -----------------------


Attest:

/s/ EDWARD R. JOHNSON
-----------------------------


                                       7.
<PAGE>   8

                                   ASSIGNMENT

        For value received _______________________________ hereby sells, assigns
and transfers unto______________________________________________________________
________________________________________________________________________________
             (Please print or typewrite name and address of Assignee)
________________________________________________________________________________
the within Warrant, and does hereby irrevocably constitute and appoint _________
_________________ its attorney to transfer the within Warrant on the books of
the within named Company with full power of substitution on the premises.

Dated:
      -----------------------


                                             --------------------------------

In the Presence of:


-----------------------------


<PAGE>   9

                                    EXHIBIT A


                                SUBSCRIPTION FORM

                                                         Date:
                                                              ----------,-----
Repeater Technologies, Inc.
1150 Morse Avenue
Sunnyvale, CA 94089

Attn.: President

Ladies and Gentlemen:

         The undersigned hereby elects to exercise the Warrant issued to it by
         Repeater Technologies, Inc. and dated August 6, 1997 Warrant No. BB-18
         (the "Warrant") and to purchase thereunder ______ shares of the Series
         BB Preferred Stock of the Company (the "Shares") at a purchase price of
         Two and 64/100 Dollars ($2.64) per Share or an aggregate purchase price
         of ___________________ Dollars ($_______._______)(the "Purchase
         Price").

         The undersigned hereby elects to convert ________ percent (____%) of
         the value of the Warrant pursuant to the provisions of SECTION 4 of the
         Warrant.

         Pursuant to the terms of the Warrant, the undersigned has delivered the
Purchase Price herewith in full in cash or by certified check or wire transfer.
The undersigned also makes representations set forth on the attached EXHIBIT B
of the Warrant.


                                            Very truly yours,

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


<PAGE>   10

                                    EXHIBIT B

                            INVESTMENT REPRESENTATION

THIS AGREEMENT MUST BE COMPLETED, SIGNED AND RETURNED TO [COMPANY/ENTITY NAME]
ALONG WITH THE SUBSCRIPTION FORM BEFORE THE PREFERRED STOCK ISSUABLE UPON
EXERCISE OF THE WARRANT DATED JULY __, 1997 WILL BE ISSUED.

                                                      Date:
                                                           -----------,------

Repeater Technologies, Inc.
1150 Morse Avenue
Sunnyvale, CA 94089

Attn.: President

Ladies and Gentlemen:

         The undersigned, _______________ ("Purchaser"), intends to acquire up
to ________ shares of the Series BB Preferred Stock (the "Preferred Stock") of
Repeater Technologies, Inc. (the "Company") from the Company pursuant to the
exercise or conversion of certain Warrants to purchase Preferred Stock held by
Purchaser. The Preferred Stock will be issued to Purchaser in a transaction not
involving a public offering and pursuant to an exemption from registration under
the Securities Act of 1933, as amended (the "1933 Act") and applicable state
securities laws. In connection with such purchase and in order to comply with
the exemptions from registration relied upon by the Company, Purchaser
represents, warrants and agrees as follows:

Purchaser is acquiring the Preferred Stock for its own account, to hold for
investment, and Purchaser shall not make any sale, transfer or other disposition
of the Preferred Stock in violation of the 1933 Act or the General Rules and
Regulations promulgated thereunder by the Securities Exchange Commission (the
"SEC") or in violation of any applicable state securities law.

Purchaser has been advised that the Preferred Stock has not been registered
under the 1933 Act or state securities laws on the ground that this transaction
is exempt from registration, and that reliance by the Company on such
exemptions is predicated in part on Purchaser's representations set forth in
this letter.

Purchaser has been informed that under the 1933 Act, the Preferred Stock must be
held indefinitely unless it is subsequently registered under the 1933 Act or
unless an exemption from such registration (such as Rule 144) is available with
respect to any proposed transfer or disposition by Purchaser of the Preferred
Stock. Purchaser further agrees that the Company may refuse to permit Purchaser
to sell, transfer or dispose of the Preferred Stock (excepted as permitted under
Rule 144) unless there is in effect a registration statement under the 1933 Act
and any applicable state securities laws covering such transfer, or unless
Purchaser furnishes an opinion of counsel reasonable satisfactory to counsel for
the Company, to the effect that such registration is not required.

Purchaser also understands and agrees that there will be placed on the
certificate(s) for the Preferred Stock, or any substitutions therefor, a legend
stating in substance:

"The shares represented by this certificate have not been registered under the
Securities Act of 1933, as amended (the "Securities Act"), or any state
securities laws. These shares have been acquired for investment and may not be
sold or otherwise transferred in the absence of an effective registration
statement for these shares under the Securities Act and applicable state
securities laws, or an opinion of counsel satisfactory to the Company that
registration is not required and that an applicable exemption is available."

<PAGE>   11
Purchaser has carefully read this letter and has discussed its requirements and
other applicable limitations upon Purchaser's resale of the Preferred Stock with
Purchaser's counsel.

                                       Very truly yours,

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