<PAGE>   1
   

                                                                   EXHIBIT 10.28
    



                           LOAN AND SECURITY AGREEMENT
   

         THIS LOAN AND SECURITY AGREEMENT (this "Loan Agreement") is made as of
February 7, 1996 among METRICOM, INC. ("Lender"), OVERALL WIRELESS
COMMUNICATIONS CORPORATION ("Borrower") and Jean Warren (with respect to Section
11.9 only).
    

                                    RECITALS

                  Borrower wishes to obtain credit from Lender, and Lender
desires to extend credit to Borrower. This Agreement sets forth the terms on
which Lender will advance credit to Borrower, and Borrower will repay the
amounts owing to Lender.

                                    AGREEMENT

         The parties to this Agreement agree as follows:

1.       DEFINITIONS AND CONSTRUCTION.

         1.1      DEFINITIONS. Unless otherwise defined herein, capitalized
terms have the meanings given them in the Option Agreement (as defined below).
As used in this Agreement, the following terms will have the following
definitions:

                  (a)      "ACCOUNTS" means all presently existing and hereafter
arising accounts, contract rights, and all other forms of obligations owing to
Borrower arising out of the sale or lease of goods (including, without
limitation, the licensing of software and other technology) or the rendering of
services by Borrower, whether or not earned by performance, and any and all
credit insurance, guaranties, and other security therefor, as well as all
merchandise returned to or reclaimed by Borrower and Borrower's Books relating
to any of the foregoing.

                  (b)      "BORROWER'S BOOKS" means all of Borrower's books and
records including ledgers; records concerning Borrower's assets or liabilities,
the Collateral, business operations or financial condition; and all computer
programs, or tape files, and the equipment containing such information.

                  (c)      "CODE" means the California Uniform Commercial Code.

                  (d)      "COLLATERAL" means the property described on EXHIBIT
A attached hereto.

_____________________

   
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.
    
<PAGE>   2
                  (e)      "EQUIPMENT" means all present and future machinery,
equipment, tenant improvements, furniture, fixtures, vehicles, tools, parts and
attachments in which Borrower has any interest.

                  (f)      "GAAP" means generally accepted accounting principles
as in effect from time to time.

                  (g)      "INSOLVENCY PROCEEDING" means any proceeding
commenced by or against any person or entity under any provision of the United
States Bankruptcy Code, as amended, or under any other bankruptcy or insolvency
law, including assignments for the benefit of creditors, formal or informal
moratoria, compositions, extension generally with its creditors, or proceedings
seeking reorganization, arrangement, or other relief.

                  (h)      "INVENTORY" means all present and future inventory in
which Borrower has any interest, including merchandise, raw materials, parts,
supplies, packing and shipping materials, work in process and finished products
intended for sale or lease or to be furnished under a contract of service, of
every kind and description now or at any time hereafter owned by or in the
custody or possession, actual or constructive, of Borrower, including such
inventory as is temporarily out of its custody or possession or in transit and
including any returns upon any accounts or other proceeds, including insurance
proceeds, resulting from the sale or disposition of any of the foregoing and any
documents of title representing any of the above, and Borrower's Books relating
to any of the foregoing.

                  (i)      "IRC" means the Internal Revenue Code of 1986, as
amended, and the regulations thereunder.

                  (j)      "LIEN" means any mortgage, lien, deed of trust,
charge, pledge, security interest or other encumbrance.

                  (k)      "LOAN DOCUMENTS" means, collectively, this Agreement,
the Note, the Pledge Agreement and any other agreement entered into between
Borrower and Lender in connection with this Agreement, all as amended or
extended from time to time.

                  (l)      "MATERIAL ADVERSE EFFECT" means a material adverse
effect on (1) the business operations or condition (financial or otherwise) of
Borrower or (2) the ability of Borrower to repay the Obligations or otherwise
perform its obligations under the Loan Documents.

                  (m)      "MATURITY DATE" means [*].

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

                                       2.
    
<PAGE>   3
                  (n)      "NEGOTIABLE COLLATERAL" means all of Borrower's
present and future letters of credit of which it is a beneficiary, notes,
drafts, instruments, securities, documents of title, and chattel paper, and
Borrower's Books relating to any of the foregoing.

                  (o)      "OBLIGATIONS" means all debt, principal, interest,
Lender's costs and 1expenses in the enforcement of this Agreement, and other
amounts owed to Lender by Borrower pursuant to this Agreement or any other Loan
Document, whether absolute or contingent, due or to become due, now existing or
hereafter arising, including any interest that accrues after the commencement of
an Insolvency Proceeding.
   

                  (p)      "OPTION AGREEMENT" that certain Option Agreement and
Agreement and Plan of Reorganization among Lender, Borrower and Jean Warren
dated as of the date hereof.
    

                  (q)      "PERSON" means any individual, sole proprietorship,
partnership, limited liability company, joint venture, trust, unincorporated
organization, association, corporation, institution, public benefit corporation,
firm, joint stock company, estate, entity or governmental agency.
   

                  (r)      "PLEDGE AGREEMENT" means that certain Stock Pledge
Agreement dated as of the date hereof between Jean Warren and Lender.
    

                  (s)      "RESPONSIBLE OFFICER" means each of the Chief
Executive Officer, the Chief Financial Officer and the Controller of Borrower.

         1.2      ACCOUNTING TERMS. All accounting terms not specifically
defined herein will be construed in accordance with GAAP and all calculations
made hereunder will be made in accordance with GAAP. When used herein, the term
"financial statements" includes the notes and schedules thereto.

2.       LOAN AND TERMS OF PAYMENT.

         2.1      ADVANCES.

                  (a)      At any time from the date hereof through [*],
Borrower may from time to time request advances (each a "Level One Advance" and
collectively, the "Level One Advances") from Lender [*]. To evidence each Level
One Advance, Borrower will deliver to Lender, at the time of each Level One
Advance request, an invoice for the equipment to be purchased or other costs
relating to construction, deployment and operation. The Level One Advances will
be used only to purchase equipment for and pay construction, operation and other
costs associated with achieving and maintaining Ten Percent Completion.

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.
    

                                       3.
<PAGE>   4
                  (b)      At any time following Ten Percent Completion through
the termination of the Option Agreement, Borrower may from time to time request
advances (each a "Level Two Advance" and collectively, the "Level Two Advances")
from Lender [*]. To evidence each Level Two Advance, Borrower will deliver to
Lender, at the time of each Level Two Advance request, an invoice for the
equipment to be purchased or other costs relating to construction, deployment
and operation to be paid. The Level Two Advances will be used only to purchase
equipment for and pay construction, operation and other costs associated with
achieving and maintaining Forty Percent Completion.

                  (c)      All Advances will be payable in full in one
installment of principal, plus all accrued interest, on the Maturity Date.

                  (d)      When Borrower desires to obtain an Advance, Borrower
will notify Lender by facsimile transmission to be received no later than [*]
before the day on which the Advance is to be made. Such notice will be
substantially in the form of EXHIBIT B. The notice will be signed by a
Responsible Officer and include a copy of the invoices described in this 
Section 2.1. If all applicable conditions set forth in Section 3 have been met, 
Lender will loan to Borrower, by check or wire transfer as Borrower may 
specify, cash in the amount requested by the Advance within ten days of 
receipt of such notice.

                  (e)      [*].

         2.2      INTEREST RATE, PAYMENT, AND CALCULATION.

                  Except as set forth in this Section 2.2, any Advances will
bear interest, on the outstanding principal balance, at a rate equal to [*] per
annum. All Obligations will bear interest, from and after the occurrence of an
Event of Default, at a rate [*]. Interest hereunder will be due and payable
together with the principal on the Maturity Date. All interest chargeable under
the Loan Documents will be computed on the basis of a 360-day year for the
actual number of days elapsed.

3.       CONDITIONS OF LOANS.

         3.1      CONDITIONS PRECEDENT TO INITIAL LEVEL ONE ADVANCE. The
obligation of Lender to make the initial Level One Advance is subject to the
condition precedent that Lender will have received, in form and substance
reasonably satisfactory to Lender, the following:

                  (a)      this Agreement and the Note;

                  (b)      the Pledge Agreement;

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

                                       4.
    
<PAGE>   5
                  (c)      a governmental certificate as to the corporate
standing of Borrower in its jurisdiction of incorporation;

                  (d)      a certificate of Borrower's Secretary with respect to
Borrower's Certificate of Incorporation and Bylaws, and authorizing resolutions
of Borrower's board of directors, and containing incumbency information and
specimen signatures of Responsible Officers;

                  (e)      financing statements (Forms UCC-1);

                  (f)      insurance certificate; and

                  (g)      such other documents, and completion of such other
matters, as Lender may reasonably deem necessary or appropriate.

                  3.2      CONDITIONS PRECEDENT TO INITIAL LEVEL TWO ADVANCE.
The obligation of Lender to make the initial Level Two Advance is subject to the
condition precedent that Borrower will have complied with the conditions
precedent to all Level One Advances.

                  3.3      CONDITIONS PRECEDENT TO ALL ADVANCES. The obligation
of Lender to make each Advance, including the initial Advance, is further
subject to the following conditions:

                           (a)      timely receipt by Lender of the
Payment/Advance Request Form as provided in Section 2.1; and

                           (b)      the representations and warranties of
Borrower contained in Section 5 will be true and correct in all material
respects on and as of the date of such Payment/Advance Request Form and on the
effective date of each Advance as though made at and as of each such date, and
no Event of Default will have occurred and be continuing, or would result from
such Advance. The making of each Advance will be deemed to be a representation
and warranty by Borrower on the date of such Advance as to the accuracy of the
facts referred to in this Section 3.3(b).

4.       CREATION OF SECURITY INTEREST.

         4.1      GRANT OF SECURITY INTEREST. Borrower hereby grants to Lender a
continuing security interest in all presently existing and hereafter acquired or
arising Collateral in order to secure prompt repayment of any and all
Obligations and in order to secure prompt performance by Borrower of each of its
covenants and duties under the Loan Documents. Such security interest
constitutes a valid, first priority security interest in the presently existing
Collateral, and will constitute a valid, first priority security interest in
Collateral acquired after the date hereof.

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

                                       5.
    
<PAGE>   6
         4.2      DELIVERY OF ADDITIONAL DOCUMENTATION REQUIRED. Borrower will
from time to time execute and deliver to Lender, at the request of Lender, all
Negotiable Collateral, all financing statements and other documents that Lender
may reasonably request, in form satisfactory to Lender, to perfect and continue
perfected Lender's security interests in the Collateral and in order to fully
consummate all of the transactions contemplated under the Loan Documents.

         4.3      RIGHT TO INSPECT. Lender (through any of its officers,
employees, or agents) will have the right, upon reasonable prior notice, from
time to time during Borrower's usual business hours, to inspect Borrower's Books
and to make copies thereof and to check, test, and appraise the Collateral in
order to verify Borrower's financial condition or the amount, condition of, or
any other matter relating to, the Collateral.

5.       REPRESENTATIONS AND WARRANTIES.

         Borrower represents and warrants to Lender as follows:

         5.1      INCORPORATION OF REPRESENTATIONS AND WARRANTIES. The
representations and warranties of Borrower contained in Section 3 of the Option
Agreement are hereby incorporated herein by reference.

         5.2      FULL DISCLOSURE. No representation, warranty or other
statement made by Borrower in any certificate or written statement furnished to
Lender contains any untrue statement of a material fact or omits to state a
material fact necessary in order to make the statements contained in such
certificates or statements not misleading.

         5.3      AUTHORIZATION; BINDING OBLIGATION. Borrower has all requisite
corporate power and authority to execute and deliver this Agreement and to carry
out the provisions of this Agreement. All corporate action on the part of
Borrower, its officers, directors and stockholders necessary for the
authorization of this Agreement and the performance of all obligations of
Borrower hereunder. This Agreement is a valid and binding obligation of
Borrower, enforceable in accordance with its terms, except (a) as limited by
applicable bankruptcy, insolvency, reorganization, moratorium or other laws of
general application affecting enforcement of creditors' rights; (b) general
principles of equity that restrict the availability of equitable remedies; and
(c) as the indemnification provisions of Section 9 of this Agreement may be
limited by applicable law.

         5.4      COMPLIANCE WITH OTHER INSTRUMENTS. The execution, delivery,
and performance of and compliance with this Agreement will not, with or without
the passage of time or giving of notice, result in any such material violation,
or be in conflict with or constitute a default under any term of its certificate
of incorporation or bylaws, or of any mortgage, indenture,

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.
    

                                       6.
<PAGE>   7
contract, agreement or instrument to which it is a party or by which it is bound
or of any judgment, decree, order, writ or, to the best of Borrower's knowledge,
any statute, rule or regulation applicable to Borrower, or result in the
creation of any mortgage, pledge, lien, encumbrance or charge upon any of the
properties or assets of Borrower or the suspension, revocation, impairment,
forfeiture or nonrenewal of any permit, license, authorization or approval
applicable to Borrower, its business or operations or any of its assets or
properties.

         5.5      LITIGATION. There is no action, suit, proceeding or
investigation pending or, to the best of Borrower's knowledge, currently
threatened against Borrower or Stockholder that questions the validity of this
Agreement, the right of Borrower to enter into this Agreement or to consummate
the transactions contemplated hereby.

         5.6      COMPLIANCE WITH LAWS; PERMITS. No governmental orders,
permissions, consents, approvals or authorizations are required to be obtained
and no registrations or declarations are required to be filed in connection with
the execution and delivery by Borrower of this Agreement except such as has been
duly and validly obtained or filed, or with respect to any filings that must be
made after the execution of this Agreement, as will be filed in a timely manner.

         Lender represents and warrants to Borrower as follows:

         5.7      INCORPORATION OF REPRESENTATIONS AND WARRANTIES. The
representations and warranties of Lender contained in Section 4 of the Option
Agreement are hereby incorporated herein by reference.

         5.8      FULL DISCLOSURE. No representation, warranty or other
statement made by Lender in any certificate or written statement furnished to
Borrower contains any untrue statement of a material fact or omits to state a
material fact necessary in order to make the statements contained in such
certificates or statements not misleading.

         5.9      AUTHORIZATION; BINDING OBLIGATION. Lender has all requisite
corporate power and authority to execute and deliver this Agreement and to carry
out the provisions of this Agreement. All corporate action on the part of
Lender, its officers, directors and stockholders necessary for the authorization
of this Agreement and the performance of all obligations of Lender hereunder.
This Agreement is a valid and binding obligation of Lender, enforceable in
accordance with its terms, except (a) as limited by applicable bankruptcy,
insolvency, reorganization, moratorium or other laws of general application
affecting enforcement of creditors' rights; (b) general principles of equity
that restrict the availability of equitable remedies; and (c) as the
indemnification provisions of Section 9 of this Agreement may be limited by
applicable law.

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    

                                       7.
<PAGE>   8
         5.10     COMPLIANCE WITH OTHER INSTRUMENTS. The execution, delivery,
and performance of and compliance with this Agreement will not, with or without
the passage of time or giving of notice, result in any such material violation,
or be in conflict with or constitute a default under any term of its certificate
of incorporation or bylaws, or of any mortgage, indenture, contract, agreement
or instrument to which it is a party or by which it is bound or of any judgment,
decree, order, writ or, to the best of Lender's knowledge, any statute, rule or
regulation applicable to Lender, or result in the creation of any mortgage,
pledge, lien, encumbrance or charge upon any of the properties or assets of
Lender or the suspension, revocation, impairment, forfeiture or nonrenewal of
any permit, license, authorization or approval applicable to Lender, its
business or operations or any of its assets or properties.

         5.11     LITIGATION. There is no action, suit, proceeding or
investigation pending or, to the best of Lender's knowledge, currently
threatened against Lender that questions the validity of this Agreement, the
right of Lender to enter into this Agreement or to consummate the transactions
contemplated hereby.

         5.12     COMPLIANCE WITH LAWS; PERMITS. No governmental orders,
permissions, consents, approvals or authorizations are required to be obtained
and no registrations or declarations are required to be filed in connection with
the execution and delivery by Lender of this Agreement except such as has been
duly and validly obtained or filed, or with respect to any filings that must be
made after the execution of this Agreement, as will be filed in a timely manner.

6.       AFFIRMATIVE COVENANTS.

         Borrower covenants and agrees that, until payment in full of all
outstanding Obligations, and for so long as Lender may have any commitment to
make an Advance hereunder, Borrower will do all of the following:

         6.1      GOOD STANDING. Borrower will maintain its corporate existence
and good standing in its jurisdiction of incorporation and maintain
qualification in each jurisdiction in which the failure to so qualify could have
a Material Adverse Effect. Borrower will maintain, to the extent consistent with
prudent management of Borrower's business, in force all licenses, approvals and
agreements, the loss of which could have a Material Adverse Effect.

         6.2      GOVERNMENT COMPLIANCE. Borrower will comply with all statutes,
laws, ordinances and government rules and regulations to which it is subject,
noncompliance with which could have a Material Adverse Effect or a material
adverse effect on the Collateral or the priority of Lender's Lien on the
Collateral.

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    

                                       8.
<PAGE>   9
         6.3      TAXES. Borrower will make due and timely payment or deposit of
all material federal, state, and local taxes, assessments, or contributions
required of it by law, and will execute and deliver to Lender, on demand,
appropriate certificates attesting to the payment or deposit thereof; and
Borrower will make timely payment or deposit of all material tax payments and
withholding taxes required of it by applicable laws, including, but not limited
to, those laws concerning F.I.C.A., F.U.T.A., state disability, and local,
state, and federal income taxes, and will, upon request, furnish Lender with
proof satisfactory to Lender indicating that Borrower has made such payments or
deposits; provided that Borrower need not make any payment if the amount or
validity of such payment is contested in good faith by appropriate proceedings
and is reserved against (to the extent required by GAAP) by Borrower.

         6.4      INSURANCE.

                  (a)      Borrower, at its expense, will maintain liability
insurance and will keep the Collateral insured against loss or damage by fire,
theft, explosion, sprinklers, and all other hazards and risks, and in such
amounts, as described in the original Disclosure Schedule.

                  (b)      All such policies of insurance will be in such form,
with such companies, and in such amounts as reasonably satisfactory to Lender.
All such policies of property insurance will contain a lender's loss payable
endorsement, in a form satisfactory to Lender, showing Lender as an additional
loss payee thereof and all liability insurance policies will show the Lender as
an additional insured, and will specify that the insurer must give at least 20
days' notice to Lender before canceling its policy for any reason. Borrower will
deliver to Lender certified copies of such policies of insurance and evidence of
the payments of all premiums therefor. All proceeds payable under any such
policy will, at the option of Lender, be payable to Lender to be applied on
account of the Obligations.

         6.5      FURTHER ASSURANCES. At any time and from time to time Borrower
will execute and deliver such further instruments and take such further action
as may reasonably be requested by Lender to effect the purposes of this
Agreement.

7.       EVENTS OF DEFAULT.

         Any one or more of the following events will constitute an Event of
Default by Borrower under this Agreement:

         7.1      PAYMENT DEFAULT. If Borrower fails to pay, when due, any of
the Obligations.


   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    

                                       9.
<PAGE>   10
         7.2      COVENANT DEFAULT.
   

                  (a)      If Borrower or Jean Warren commits a material Breach
under the Option Agreement and as to any Breach that can be cured, has failed 
to cure such default within [*] after Borrower receives notice thereof or any 
officer of Borrower becomes aware thereof (provided that no Advances will be 
required to be made during such cure period), or

                  (b)      If Borrower or Jean Warren fails or neglects to 
perform, keep, or observe any other material term, provision, condition, 
covenant, or agreement contained in this Agreement, in any of the Loan 
Documents, or in any other present or future agreement between Borrower and 
Lender and as to any default under such other term, provision, condition, 
covenant or agreement that can be cured, has failed to cure such default within 
[*] after Borrower receives notice thereof or any officer of Borrower becomes 
aware thereof (provided that no Advances will be required to be made during 
such cure period);
    

         7.3      ATTACHMENT. If any material portion of Borrower's assets is
attached, seized, subjected to a writ or distress warrant, or is levied upon, or
comes into the possession of any trustee, receiver or person acting in a similar
capacity and such attachment, seizure, writ or distress warrant or levy has not
been removed, discharged or rescinded within [*], or if Borrower is enjoined,
restrained, or in any way prevented by court order from continuing to conduct
all or any material part of its business affairs, or if a judgment or other
claim becomes a lien or encumbrance upon any material portion of Borrower's
assets, or if a notice of lien, levy, or assessment is filed of record with
respect to any of Borrower's assets by the United States Government, or any
department, agency, or instrumentality thereof, or by any state, county,
municipal, or governmental agency, and the same is not paid within [*] after
Borrower receives notice thereof, provided that none of the foregoing will
constitute an Event of Default where such action or event is stayed or an
adequate bond has been posted pending a good faith contest by Borrower (provided
that no Advances will be required to be made during such cure period);

         7.4      INSOLVENCY. If an Insolvency Proceeding is commenced by
Borrower, or if an Insolvency Proceeding is commenced against Borrower and is
not dismissed or stayed within [*] (provided that no Advances will be made prior
to the dismissal of such Insolvency Proceeding); and

         7.5      MISREPRESENTATIONS. If any material misrepresentation or
material misstatement exists now or hereafter in any warranty or representation
set forth herein or in any certificate delivered to Lender by any Responsible
Officer pursuant to this Agreement or to induce Lender to enter into this
Agreement or any other Loan Document, and as to a misrepresentation or
misstatement that can be cured, Borrower fails to correct such misrepresentation
or misstatement to Lender's satisfaction within [*] after Borrower receives
notice thereof or any officer of

_______________
   

*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.
    

                                       10.
<PAGE>   11
Borrower becomes aware thereof (provided that no Advances will be required to be
made during such cure period).

8.       LENDER'S RIGHTS AND REMEDIES.

         8.1      RIGHTS AND REMEDIES. Upon the occurrence and during the
continuance of an Event of Default, Lender may, at its election, without notice
of its election and without demand (but subject to FCC approval, if required),
do any one or more of the following, all of which are authorized by Borrower:

                  (a)      Declare all Obligations, whether evidenced by this
Agreement, by any of the other Loan Documents, or otherwise, immediately due and
payable (provided that upon the occurrence of an Event of Default described in
Section 7.4 all Obligations will become immediately due and payable without any
action by Lender);

                  (b)      Cease advancing money or extending credit to or for
the benefit of Borrower under this Agreement or under any other agreement
between Borrower and Lender;

                  (c)      Settle or adjust disputes and claims directly with
account debtors for amounts, upon terms and in whatever order that Lender
reasonably considers advisable;

                  (d)      Without notice to or demand upon Borrower, make such
payments and do such acts as Lender considers necessary or reasonable to protect
its security interest in the Collateral. Borrower agrees to assemble the
Collateral if Lender so requires, and to make the Collateral available to Lender
as Lender may designate. Borrower authorizes Lender to enter the premises where
the Collateral is located, to take and maintain possession of the Collateral, or
any part of it, and to pay, purchase, contest, or compromise any encumbrance,
charge, or lien which in Lender's determination appears to be prior or superior
to its security interest and to pay all expenses incurred in connection
therewith. With respect to any of Borrower's owned premises, Borrower hereby
grants Lender a license to enter into possession of such premises and to occupy
the same, without charge, for up to 120 days in order to exercise any of
Lender's rights or remedies provided herein, at law, in equity, or otherwise;

                  (e)      Without notice to Borrower set off and apply to the
Obligations any and all indebtedness at any time owing to or for the credit or
the account of Borrower held by Lender;

                  (f)      Ship, reclaim, recover, store, finish, maintain,
repair, prepare for sale, advertise for sale, and sell (in the manner provided
for herein) the Collateral. Lender is hereby granted a license or other right,
solely pursuant to the provisions of this Section 8.1, to use, without charge,
Borrower's labels, patents, copyrights, rights of use of any name, trade
secrets,

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    

                                       11.
<PAGE>   12
trade names, trademarks, service marks, and advertising matter, or any property
of a similar nature, as it pertains to the Collateral, in completing production
of, advertising for sale, and selling any Collateral and, in connection with
Lender's exercise of its rights under this Section 8.1, Borrower's rights under
all licenses and all franchise agreements will inure to Lender's benefit;

                  (g)      Sell the Collateral at either a public or private
sale, or both, by way of one or more contracts or transactions, for cash or on
terms, in such manner and at such places (including Borrower's premises) as
Lender determines is commercially reasonable;

                  (h)      Lender may credit bid and purchase at any public
sale; and

                  (i)      Any deficiency that exists after disposition of the
Collateral as provided above will be paid immediately by Borrower.

         8.2      POWER OF ATTORNEY. Effective only upon the occurrence and
during the continuance of an Event of Default, Borrower hereby irrevocably
appoints Lender (and any of Lender's designated officers, or employees) as
Borrower's true and lawful attorney to: (a) send requests for verification of
Accounts or notify account debtors of Lender's security interest in the
Accounts; (b) endorse Borrower's name on any checks or other forms of payment or
security that may come into Lender's possession; (c) sign Borrower's name on any
invoice or bill of lading relating to any Account, drafts against account
debtors, schedules and assignments of Accounts, verifications of Accounts, and
notices to account debtors; (d) make, settle, and adjust all claims under and
decisions with respect to Borrower's policies of insurance; and (e) settle and
adjust disputes and claims respecting the accounts directly with account
debtors, for amounts and upon terms which Lender determines to be reasonable;
provided Lender may exercise such power of attorney to sign the name of Borrower
on any of the documents described in Section 4.2 regardless of whether an Event
of Default has occurred. The appointment of Lender as Borrower's attorney in
fact, and each and every one of Lender's rights and powers, being coupled with
an interest, is irrevocable until all of the Obligations have been fully repaid
and performed and Lender's obligation to provide advances hereunder is
terminated.

         8.3      ACCOUNTS COLLECTION. Effective only upon the occurrence and
during the continuance of an Event of Default, Lender may notify any Person
owing funds to Borrower of Lender's security interest in such funds and verify
the amount of such Account. Borrower will collect all amounts owing to Borrower
for Lender, receive in trust all payments as Lender's trustee, and immediately
deliver such payments to Lender in their original form as received from the
account debtor, with proper endorsements for deposit.

         8.4      LENDER'S LIABILITY FOR COLLATERAL. So long as Lender complies
with reasonable business practices, Lender will not in any way or manner be
liable or responsible for: (a) the

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    

                                       12.
<PAGE>   13
safekeeping of the Collateral; (b) any loss or damage thereto occurring or
arising in any manner or fashion from any cause; (c) any diminution in the value
thereof; or (d) any act or default of any carrier, warehouseman, bailee,
forwarding agency, or other person whomsoever. All risk of loss, damage or
destruction of the Collateral will be borne by Borrower.

         8.5      REMEDIES CUMULATIVE. Lender's rights and remedies under this
Agreement, the Loan Documents, and all other agreements will be cumulative.
Lender will have all other rights and remedies not inconsistent herewith as
provided under the Code, by law, or in equity. No exercise by Lender of one
right or remedy will be deemed an election, and no waiver by Lender of any Event
of Default on Borrower's part will be deemed a continuing waiver. No delay by
Lender will constitute a waiver, election, or acquiescence by it. No waiver by
Lender will be effective unless made in a written document signed on behalf of
Lender and then will be effective only in the specific instance and for the
specific purpose for which it was given.

         8.6      DEMAND; PROTEST. Borrower waives demand, protest, notice of
protest, notice of default or dishonor, notice of payment and nonpayment, notice
of any default, nonpayment at maturity, release, compromise, settlement,
extension, or renewal of accounts, documents, instruments, chattel paper, and
guarantees at any time held by Lender on which Borrower may in any way be
liable.

9.       INDEMNIFICATION.

         Borrower will defend, indemnify and hold harmless Lender and its
officers, employees, and agents against: (a) all obligations, demands, claims,
and liabilities claimed or asserted by any other party in connection with the
transactions contemplated by this Agreement; and (b) all losses or costs and
expenses in any way suffered, incurred, or paid by Lender as a result of or in
any way arising out of, following, or consequential to transactions between
Lender and Borrower whether under this Agreement, or otherwise (including
without limitation reasonable attorneys fees and expenses), except for losses
caused by Lender's gross negligence or willful misconduct.

10.      ADDITIONAL AGREEMENTS.
   

         10.1     BREACH BY LENDER. In the event Lender fails to make any
advance when due pursuant to this Agreement, and Lender fails to cure such
breach within [*] business days after Borrower gives Lender notice thereof,
Borrower will be entitled to [*]. The foregoing [*] will be suspended during
any period during which there exists a good faith dispute concerning the
compliance with the requirements of this Agreement of Borrower's request for
the Advance in question.
    

         10.2     TERMINATION OF OPTION AGREEMENT.

                  (a)      In the event Lender terminates the Option in
accordance with Section 1.4(b)(2) of the Option Agreement, Borrower terminates
the Option Agreement in accordance with Section 8.1(d) of the Option Agreement
or the Option expires unexercised and in any such case there is no material
Breach by Borrower or Jean Warren, Lender will promptly pay Borrower a


   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.
    

                                       13.
<PAGE>   14
termination fee equal to the greater of (1) $1,000,000 plus all Level One
Advances then outstanding (including all accrued but unpaid interest with
respect thereto) and (2) the amount of all principal and accrued but unpaid
interest under this Agreement.

                  (b)      In the event either party terminates the Option
Agreement pursuant to Section 8.1(b) of the Option Agreement, Lender will
promptly pay Borrower a termination fee equal to (1) fifty percent (50%) of the
aggregate amount of principal and accrued but unpaid interest then outstanding
minus (2) $350,000.

                  (c)      Any such termination fee may be paid, at the
discretion of Lender, in cash or through cancellation of any amount owed by
Borrower or Jean Warren to Lender or through a combination thereof.

   


                  10.3     ADDITIONAL PAYMENT.  In the event lender is required
to make an Additional Payment, and any portion of the proceeds hereunder are
used to fund operations, then, notwithstanding anything to the contrary
contained in the Option Agreement, "Acquisition Consideration," for purposes of
the Option Agreement, will mean the sum of (a) [*], and (e) interest at the 
annual rate of [*] on the sum of (a), (b), (c) and (d) above from the Closing 
Date until the date of sale.

    

11.      MISCELLANEOUS.

         11.1     GOVERNING LAW. This Agreement will be governed in all respects
by the laws of the State of California as such laws are applied to agreements
between California residents entered into and performed entirely in California.

         11.2     SURVIVAL. The representations, warranties, covenants and
agreements made herein will survive any investigation made by Borrower and the
transactions contemplated hereby. All statements as to factual matters contained
in any certificate or other instrument delivered by or on behalf of Borrower
pursuant hereto in connection with the transactions contemplated hereby will be
deemed to be representations and warranties by Borrower hereunder solely as of
the date of such certificate or instrument.

         11.3     SUCCESSORS AND ASSIGNS. Except as otherwise expressly provided
herein, the provisions hereof will inure to the benefit of, and be binding upon,
the successors, assigns, heirs, executors and administrators of the parties
hereto.

         11.4     ENTIRE AGREEMENT. This Agreement and the Exhibits hereto
constitute the full and entire understanding and agreement between the parties
with regard to the subjects hereof and no party will be liable or bound to any
other in any manner by any representations, warranties, covenants and agreements
except as specifically set forth herein and therein.

         11.5     SEVERABILITY. In case any provision of the Agreement is
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions will not in any way be affected or impaired thereby.


   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    
                                       14.
<PAGE>   15
         11.6     AMENDMENT. This Agreement may be amended only by a writing
executed by Borrower and Lender.

         11.7     DELAYS OR OMISSIONS. It is agreed that no delay or omission to
exercise any right, power or remedy accruing to any party, upon any breach,
default or noncompliance by another party under this Agreement will impair any
such right, power or remedy, nor will it be construed to be a waiver of any such
breach, default or noncompliance, or any acquiescence therein, or of any similar
breach, default or noncompliance thereafter occurring. It is further agreed that
any waiver, permit, consent or approval of any kind or character on any party's
part of any breach, default or noncompliance under this Agreement or any waiver
on such party's part of any provisions or conditions of this Agreement must be
in writing and will be effective only to the extent specifically set forth in
such writing. All remedies under this Agreement or otherwise afforded to any
party, will be cumulative and not alternative.

         11.8     NOTICES. Any notice or other communication required or
permitted to be delivered to any party under this Agreement will be in writing
and will be deemed properly delivered, given and received when delivered (by
hand, by certified mail with return receipt requested, by courier or express
delivery service or by telecopier) to the address or telecopier number set forth
beneath the name of such party below (or to such other address or telecopier
number as such party shall have specified in a written notice given to the other
parties hereto):

                                if to Lender:

                                     Metricom, Inc.
                                     980 University Avenue
                                     Los Gatos, CA  95030
                                     Attention:  William D. Swain
                                     Telecopier:  (408) 399-8274

                                with a copy to:

                                     Cooley Godward Castro Huddleson & Tatum
                                     One Maritime Plaza, 20th Floor
                                     San Francisco, CA  94111-3580
                                     Attention:  Kenneth L. Guernsey
                                     Telecopier:  (415) 951-3699

   
                                if to Borrower:
                                        
                                     Jean Warren
                                     [*]
    


________________

   
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed 
         separately with the Commission.
    

                                       15.
<PAGE>   16
                         with a copy to:

                                McAfee & Taft
                                Tenth Floor, Two Leadership Square
                                211 N. Robinson
                                Oklahoma City, OK 73102
                                Attention:  Gary F. Fuller
                                Facsimile:  (405) 235-0439

                                and

                                Lukas, McGowan, Nace & Gutierrez, 
                                  Chartered
                                1111 Nineteenth Street, NW
                                Suite 1200
                                Washington, DC 20036
                                Attention:  Gerald S. McGowan and 
                                              George L. Lyon, Jr.
                                Facsimile:  (202) 842-4485

         11.9     EXPENSES. Except as provided in Section 11.10, Lender will pay
all costs and expenses that it incurs, and Jean Warren will pay all costs and
expenses that Borrower incurs (either directly or through a capital contribution
to Borrower in an amount equal to any costs and expenses paid by Borrower), with
respect to the negotiation, execution, delivery and performance of this
Agreement and the Exhibits hereto.

         11.10    ATTORNEYS' FEES. In the event that any dispute among the
parties to this Agreement should result in litigation, the prevailing party in
such dispute will be entitled to recover from the losing party or parties all
fees, costs and expenses of enforcing any right of such prevailing party under
or with respect to this Agreement, including without limitation, such reasonable
fees and expenses of attorneys and accountants, which will include, without
limitation, all fees, costs and expenses of appeals.

         11.11    REMEDIES CUMULATIVE; SPECIFIC PERFORMANCE. The rights and
remedies of the parties hereto will be cumulative (and not alternative). In the
event of any breach or threatened breach by any party of any covenant,
obligation or other provision set forth in this Agreement, the other party will
be entitled (in addition to any other remedy that may be available to it) to (a)
a decree or order of specific performance or mand amus to enforce the observance
and performance of such covenant, obligation or other provision, and (b) an
injunction restraining such breach or threatened breach. Neither party will be
required to provide any bond or other security in connection with any such
decree, order or injunction or in connection with any related action or
proceeding.

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    

                                       16.
<PAGE>   17
         11.12    TITLES AND SUBTITLES. The titles of the sections and
subsections of the Agreement are for convenience of reference only and are not
to be considered in construing this Agreement.

         11.13    COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which will be an original, but all of which together will
constitute one instrument.

   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    

                                       17.
<PAGE>   18
                  IN WITNESS WHEREOF, the parties hereto have executed this
Agreement as of the date first above written.

METRICOM, INC.                                  OVERALL WIRELESS COMMUNICATIONS
                                                CORPORATION

   
By:      /s/ Gary M. Green                      By:      /s/ Jean Warren
    ---------------------------------              ----------------------------
Name:          Gary M. Green                    Name:           Jean Warren
Title:         Chief Operating Officer          Title:          President
    



 /s/ Jean Warren
-------------------------------------
Jean Warren




____________________

   
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.
    
<PAGE>   19
                                    EXHIBIT A

                                   COLLATERAL

         The Collateral will consist of all right, title and interest of
Borrower in and to the following:

         (a)      All goods and equipment now owned or hereafter acquired,
including, without limitation, all machinery, fixtures, vehicles (including
motor vehicles and trailers), base stations and any interest in any of the
foregoing, and all attachments, accessories, accessions, replacements,
substitutions, additions, and improvements to any of the foregoing, wherever
located;

         (b)      All inventory, now owned or hereafter acquired, including,
without limitation, all merchandise, raw materials, parts, supplies, packing and
shipping materials, work in process and finished products including such
inventory as is temporarily out of Borrower's custody or possession or in
transit and including any returns upon any accounts or other proceeds, including
insurance proceeds, resulting from the sale or disposition of any of the
foregoing and any documents of title representing any of the above, and
Borrower's Books relating to any of the foregoing;

         (c)      All contract rights and general intangibles now owned or
hereafter acquired, including, without limitation, goodwill, trademarks,
servicemarks, trade styles, trade names, patents, patent applications, leases,
license agreements (including specifically, but without limitation, all FCC
broadcast or other licenses, subject only to FCC approval of transfer),
franchise agreements, blueprints, drawings, purchase orders, customer lists,
route lists, infringements, claims, computer programs, computer discs, computer
tapes, literature, reports, catalogs, design rights, income tax refunds,
payments of insurance and rights to payment of any kind;

         (d)      All now existing and hereafter arising accounts, contract
rights, royalties, license rights and all other forms of obligations owing to
Borrower arising out of the sale or lease of goods, the licensing of technology
or the rendering of services by Borrower, whether or not earned by performance,
and any and all credit insurance, guaranties, and other security therefor, as
well as all merchandise returned to or reclaimed by Borrower and Borrower's
Books relating to any of the foregoing;

         (e)      All documents, cash, deposit accounts, securities, letters of
credit, certificates of deposit, instruments and chattel paper now owned or
hereafter acquired and Borrower's Books relating to the foregoing;
   

         (f)      All copyright rights, copyright applications, copyright
registrations and like protections in each work of authorship and derivative
work thereof, whether published or unpublished, now owned or hereafter acquired;
all trades secret rights, including all rights to unpatented inventions,
know-how, operating manuals, license rights and agreements and confidential
information, now owned or hereafter acquired; all claims for damages by way of
any past, present and future infringement of any of the forgoing; and


         (g)      Any and all claims, rights and interests in any of the above
and all substitutions for, additions and accessions to and proceeds thereof. 
    


   
_____________________
*        Confidential treatment has been requested for portions of this document
         marked with an asterisk pursuant to Rule 24b-2 under the Securities
         Exchange Act of 1934, as amended. These portions have been filed
         separately with the Commission.

    

                                      A-1.