Document:

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                                                                    EXHIBIT 4.20

                           FOURTH AMENDMENT AGREEMENT

     THIS Fourth AMENDMENT AGREEMENT (the "Agreement") is entered as of March 1,
2001 between SHARED TECHNOLOGIES CELLULAR, INC., a Delaware corporation, with
its principal place of business at 100 Great Meadow Road, Suite 104,
Wethersfield, Connecticut 06109 (the "Borrower") and MOBILE INVESTMENTS LLC, a
Connecticut limited liability company with an address at c/o Oakes, Fitzwilliams
& Co., Inc., c/o Speer & Fulvio, 60 East 42nd Street, New York, NY 10165
("Mobile") assignee of Anthony Autorino, and CITIZENS BANK OF MASSACHUSETTS
("Citizens"), for itself and as Collateral Agent.

RECITALS:

     On July 7, 1999, State Street (as predecessor in interest to Citizens) and
the Borrower entered into a Loan Agreement, as amended by that certain First
Amendment Agreement dated as of December 3, 1999, that certain Second Amendment
Agreement dated as of May 1, 2000, and that certain Third Amendment Agreement
dated August 8, 2000 (referred to herein collectively as the "Credit Agreement")
pursuant to which Citizens extended to the Borrower a Revolving Credit Facility
which is presently existing in the maximum aggregate line availability of Two
Million Five Hundred Thousand Dollars ($2,500,000.00).

      The Borrower executed and delivered to State Street on July 7, 1999 a
Secured Revolving Credit Promissory Note in the original principal amount of Ten
Million Dollars ($10,000,000.00), which was amended and restated by that certain
Amended and Restated Secured Revolving Credit Promissory Note in the original
principal amount of Five Million Dollars ($5,000,000.00) dated May 1, 2000
delivered to Citizens and that certain Amended and Restated Secured Revolving
Credit Promissory Note in the original principal amount of Two Million Five
Hundred Thousand Dollars ($2,500,000.00) dated August 8, 2000 delivered to
Citizens (collectively the "Original Note").

     Pursuant to a Nonrecourse Assignment and Acceptance agreement dated as of
March 1, 2001, Citizens assigned its interest in said Loan to Anthony Autorino,
subject to and expressly reserving its rights against the Borrower with respect
to a certain outstanding Letter of Credit No. 041082 in the original and
principal amount of $500,000, wherein GTE Mobilemet Services Corp. is the
beneficiary, expiring March 29, 2001 (the "Retained Letter of Credit"). Anthony
Autorino assigned the Loan to Mobile pursuant to a certain Nonrecourse
Assignment and Acceptance agreement dated of even date herewith, subject to the
same reservation of rights with respect to Citizens. The Borrower is obligated
to Citizens pursuant to a certain Letter of Credit Reimbursement Agreement (the
"Reimbursement Agreement").

     Citizens has agreed to hold all collateral securing the obligations of the
Borrower under the Credit Agreement and the Retained Letter of Credit as agent
for itself and Mobile, (the "Collateral Agent") pursuant to the terms of Section
X below.

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     The parties have agreed to amend the Credit Agreement and the Original Note
upon the terms and conditions set forth herein.

     NOW, THEREFORE, in consideration of the provisions herein contained,
Borrower and the Lender, each intending to be legally bound hereby, agree as
follows:

SECTION I.  AMENDMENTS TO CREDIT AGREEMENT.

     The Credit Agreement is amended hereby as follows:

     1. Citizens as Collateral Agent shall act solely with respect to the
Collateral and such of the Loan Documents as relate to the Collateral.

     All references to the "Lender", the "Secured Party" or the "Assignee" under
the Credit Agreement and the Loan Documents which relate to the Collateral, and
relate to such of the Loan Documents as relate to the Collateral, shall be
deemed amended hereby, subject to the Agency Expiration Date, to refer solely to
Citizens as Collateral Agent for Citizens and for Mobile.

           All references in the Credit Agreement to the "Lender", other than
those which relate to the Collateral and such of the Loan Documents as relate to
the Collateral as described in the immediately preceding paragraph, shall from
and after even date be deemed amended to refer to Mobile, subject, however, to
Citizens' reservation of rights, in its capacity as a lender, under the Credit
Agreement with regard to the repayment in full to it of any and all obligations
under the Retained Letter of Credit. By way of example and without limitation
hereby, Mobile shall have the right, in its sole discretion, to exercise any and
all rights and remedies to accelerate or otherwise negotiate the Revolving Line
of Credit with respect to the Borrower's or The Cellular One's failure to comply
with regard to covenants under the Credit Agreement, subject, however, to
Citizen's aforementioned reservation of rights regarding the Retained Letter of
Credit.

     2. The Borrower acknowledges and agrees that the collateral security
granted pursuant to the Credit Agreement and other Security Documents secures
the obligations evidenced by the Original Note in favor of Mobile and the
Retained Letter of Credit in favor of Citizens, and that the Collateral Agent is
holding such collateral for the benefit of Mobile and Citizens.

     3. The date "December 29, 2000" in the definition of the "Commitment
Termination Date" is hereby changed to "August 31, 2001."

     4. On the date hereof Mobile shall make an Advance of $290,000,
representing an Advance of $240,000 plus an Advance of $50,000 for the Extension
Fee more fully described in Section VII.3 below. No further Advances will be
made under the Revolving Credit Loan, and any obligation of Citizens to make any
further Advances is hereby terminated.

     5. Section 2.1(e) of the Credit Agreement regarding the Liquidity
Management Control System is deleted.

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     6. Section 2.4 of the Credit Agreement regarding prepayment is amended in
its entirety to read as follows:

           "2.4 Prepayment. The Loan may be prepaid, in full or in part, prior
           to the Commitment Termination Date, subject to Mobile's rights under
           the Letter Agreement between Mobile and Borrower of even date with
           respect to the conditional commitment of Mobile for Advances up to
           $6,000,000."

     7. Section 2.5 of the Credit Agreement is amended and restated in its
entirety as follows:

           "2.5 Rate of Interest. Interest on the Loan for the period March 1,
           2001 through the Commitment Termination Date shall be payable monthly
           on the first day of each month at the fixed rate of 12% per annum."

     8. Section 2.6 of the Credit Agreement is amended and restated in its
entirety as follows:

           "2.6 Default Rate of Interest. Notwithstanding SECTION 2.5 hereof, if
           an Event of Default shall have occurred, then in such event, to the
           extent permitted by law, the Interest Rate applicable to the Loan
           (the "Default Rate") shall be 15%."

     9. The covenants set forth in Section 5.6 through 5.12 of the Credit
Agreement are hereby deleted."

     10. The following new definitions are added to the Credit Agreement:

                    "Fourth Amendment Agreement" shall mean that certain Fourth
           Amendment Agreement entered into between the Borrower and the Lender
           dated as of March 1, 2001."

     11. Whenever notice is contemplated to be given to the "Lender" or the
"Secured Party" or the "Assignee" under the Security Documents, notice shall
also be given as follows:

           If to the Lender: Mobile Investments LLC
                             Attn:  Herbert Oakes, Jr.
                             c/o Oakes, Fitzwilliams & Co., Inc.
                             c/o Speer & Fulvio
                             60 East 42nd Street
                             New York, NY  10165

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           With a Copy to:   Brown Rudnick Freed & Gesmer
                             185 Asylum Street
                             Hartford, CT 06103
                             Attn:  Brian Courtney. Esq.

SECTION II.  AMENDMENT TO THE ORIGINAL NOTE.

     The Original Note is amended to extend the maturity date to the new
Commitment Termination Date.

SECTION III. RECONFIRMATION OF COVENANTS, REPRESENTATIVES AND WARRANTIES.

           1. The Borrower further reaffirms all of its obligations, as amended
hereby, under the Credit Agreement, and under the Security Documents.

           2. Borrower represents and agrees that, in addition to the amounts
 advanced in Section I.2. above, there is currently outstanding (a) the
 principal amount of $98,333.25 under the Credit Agreement and Original Note,
 together with accrued interest in the amount of $2,173.71 ($26.63 per diem),
 and default fees of $237,500, all of which are due and owing without setoff,
 defense, or counterclaim, and Borrower hereby waives any such setoff, defense
 or counterclaim it may have against Mobile, together with (b) its obligation to
 pay Citizens under the Credit Agreement the amount of any draw on the Retained
 Letter of Credit.

SECTION IV.  RESERVATION OF RIGHTS.

           Citizens, Mobile and the Borrower agree that:

                 i) This Agreement evidences solely the amendment of the terms
     and provisions of the Borrower's obligations under the Credit Agreement and
     the Original Note, and is not a novation or discharge thereof;

                 ii) Notwithstanding the terms hereof: Mobile and Citizens
     hereby reserves its rights against the Borrower under the Credit Agreement
     and the Original Note, as provided under the Commonwealth of Massachusetts
     law and judicial precedent, as in effect from time to time; and

                 iii) Except for this Amendment, there are no other
     understandings, express or implied between Mobile and Citizens and the
     Borrower regarding the Credit Agreement and the Original Note.

SECTION V.  EFFECT OF AMENDMENT.

           1. Except as amended hereby, the Credit Agreement and the Original
Note and all other documents entered into in connection therewith shall:

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                 a) remain in full force and effect in accordance with their
original terms and nothing herein shall be deemed to modify, abrogate, waive or
extend any other provision in the Credit Agreement and the Original Note or in
any other document, agreement or instrument executed in connection therewith or
pursuant thereto prior to the execution of this Agreement, including without
limitation any of the Borrower's liabilities to Mobile and Citizens or any of
Mobile's and Citizens' rights with respect to such liabilities; and

                 b) be in all respects ratified and affirmed.

           2. The Borrower acknowledges that all of the liabilities and
obligations of the Borrower to Mobile and Citizens now existing and hereafter
incurred are secured by the security described in the Security Documents defined
in the Credit Agreement; the Borrower further acknowledges that Mobile and
Citizens is relying upon the security described above, both as entered into on
July 9, 1999 and as entered into from time to time thereafter, as security for
the financing represented by the Liabilities and as security for all other
obligations of the Borrower to Mobile and Citizens.

SECTION VI.  WAIVER.

           Mobile hereby waives all existing Events of Default under the Credit
Agreement, with the express stipulation that this Waiver shall not operate as a
waiver of any other failure by the Borrower to meet other covenants of which
Mobile does not have notice as of the date hereof, or waiver of the failure of
the Borrower to meet the same covenants on a future occasion.

           Such Waiver shall not be construed as a course of action which would
constitute a waiver of any other default under the Credit Agreement or under any
other document executed in connection therewith or pursuant thereto. No delay in
taking any action with respect to any such default, or any other course of
action by Mobile shall affect Lender's rights to later take any such action with
respect to any such default.

SECTION VII.  GENERAL.

           1. Construction. Except as amended hereby, incorporated herein by
reference are the representations, warranties, agreements, affirmative and
negative covenants, definitions, terms and conditions all as set forth in the
Credit Agreement and the Original Note and all documents executed in connection
therewith or pursuant thereto. This Agreement, the Credit Agreement, the
Original Note, and the other Loan Documents shall be construed collectively and
in the event that any term, provision or condition of any of such documents is
inconsistent with or contradictory to any term, provision or condition of any
other such document, the terms, provisions and conditions of this Agreement
shall supersede and control the terms, provisions and conditions of the Credit
Agreement and the Original Note.

           2. Governing Law. This Agreement, the Original Note and the Credit
Agreement and all Security Documents thereunder, and the rights and obligations

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of the parties hereunder, shall in all respects be governed by, and interpreted
and determined in accordance with, the laws of the Commonwealth of Massachusetts
(excluding the laws applicable to conflicts or choice of law).

           3. Extension Fee. In consideration of this Fourth Amendment
Agreement, the Borrower shall pay, as of the date hereof, an Extension Fee to
Mobile in the amount of Fifty Thousand Dollars ($50,000.00).

SECTION VIII.  SECURITY DOCUMENTS.

The Borrower and The Cellular Hotline, Inc., each with respect to itself, by its
signature hereto, agree that:

     a) the Security Documents (defined in the Credit Agreement) are amended to
     reflect that the obligations and liabilities secured thereby are deemed
     amended pursuant to this Amendment Agreement, as incorporated therein by
     reference; and

     b) except as specifically amended hereby, the Security Documents, shall
     remain in full force and effect, in accordance with their original terms as
     previously amended, and nothing herein shall be deemed to modify, abrogate,
     waive or extend any other provision in the Security Documents, except as
     previously amended, or in any other document, agreement, or instrument
     executed in connection therewith or pursuant thereto prior to the execution
     of this Agreement, including without limitation any of the Borrower's or
     The Cellular Hotline, Inc.'s liabilities to the Lender or any of the
     Lender's rights with respect to such liabilities; and

     c) the Security Documents, as amended hereby, shall continue to secure the
     Borrower's obligations under the Credit Agreement, the Original Note, the
     Retained Letter of Credit and all other obligations of the Borrower and of
     The Cellular Hotline, Inc. to the Lender, whether now existing or hereafter
     arising.

SECTION IX. WAIVER OF TRIAL BY JURY. BORROWER, THE CELLULAR HOTLINE, INC., AND
LENDER MUTUALLY HEREBY KNOWINGLY, VOLUNTARILY AND INTENTIONALLY WAIVE THE RIGHT
TO A TRIAL BY JURY IN RESPECT OF ANY CLAIM BASED HEREIN, ARISING OUT OF, UNDER
OR IN CONNECTION WITH THIS AGREEMENT OR ANY OTHER LOAN DOCUMENTS CONTEMPLATED TO
BE EXECUTED IN CONNECTION HEREWITH OR ANY COURSE OF CONDUCT, COURSE OF DEALINGS,
STATEMENTS (WHETHER VERBAL OR WRITTEN) OR ACTIONS OF ANY PARTY. THIS WAIVER
CONSTITUTES A MATERIAL INDUCEMENT FOR THE LENDER TO ACCEPT THIS AGREEMENT AND TO
AMEND THE REVOLVING CREDIT FACILITY.

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SECTION X.  AGENCY PROVISIONS

      1. Appointment. Lenders hereby appoint Citizens as Collateral Agent and
Collateral Agent agrees to act as such for the benefit of Lenders under the
Credit Agreement and the other Loan Documents ( as defined in the Credit
Agreement) whereby the Collateral Agent has been authorized to hold all
collateral for the Loans and to exercise such powers and take such actions as
are delegated, assigned or granted to the Collateral Agent.

      2. Lender Remedies. In the event that there is a draw on the Retained
Letter of Credit that is not paid, in full, within five (5) days of date
thereof, Citizens may direct the Collateral Agent to exercise the rights in
Section X.10 below. However, nothing contained herein shall permit Collateral
Agent or Citizens to accelerate the Loan as evidence by the Original Note or
other indebtedness owing to Mobile, nor the right to waive any defaults under
the Credit Agreement. Mobile agrees that it will not have any right to enforce
or any right of collection with respect to the Retained Letter of Credit or the
Collateral granted in the Credit Agreement or Security Documents.

      3. Agreement of Requisite Lenders. The Collateral Agent shall have sole
discretion to exercise all of Lender's or Secured Parties or Assignee's rights
and remedies under the Loan Documents including, without limitation, control of
the Collateral, direction of enforcement proceedings, commencement and
prosecution of any action to pursue remedies including, without limitation,
foreclosure on all matters until such time as the earlier of (the "Agency
Expiration Date"):

            (a) the delivery to Citizens of cash collateral, in form and
      substance satisfactory to Citizens, in its sole discretion, with a face
      original amount of not less than $562,500.00, utilizing the form and
      substance of cash collateral documentation previously drafted, negotiated
      and discussed prior to even date between the Borrower, Citizens, and
      Autorino; or

            (b) the later date to occur of :

                  (i)   the date of expiration of the Retained Letter of Credit
                        without any draw by the beneficiary thereof and the
                        payment in full to Assignor of any outstanding fees,
                        interest and expenses thereunder; or

                  (ii)  the date of reimbursement in full, by wire transfer, to
                        Citizens of: any and all draws, and all interest, fees
                        and expenses under the Retained Letter of Credit; and

                  (iii) the date of payment in full of any and all obligations
                        under that certain Limited Liability Guaranty of Anthony
                        D. Autorino dated February 27, 2001, as reconfirmed
                        March 8, 2001.

Upon the satisfaction of the foregoing terms, the Agency shall terminate and
Mobile shall automatically succeed to Collateral Agent's interests under the
Credit Agreement

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and other Loan Documents. Upon any occasion requiring or permitting an approval,
consent, waiver, election or other action on the part of the Lenders, action
shall be taken by the Collateral Agent for and on behalf or for the benefit of
all Lenders, and any such action shall be binding on all Lenders.

      4. Assignment and Participation.  Neither Lender may sell, assign or grant
a participation interest in, in whole or in part, its interests, rights or
obligations in the Loans or Loan Documents.

      5. Benefit of Agreement.  The provisions of this Section X are solely for
the benefit of the Lenders and the Collateral Agent and shall not benefit in any
way or be deemed to be enforceable by the Borrower.

      6. Representations and Warranties; No Responsibility for Appraisal of
Creditworthiness. Each Lender represents and warrants that it has made its own
independent investigation of the financial condition and affairs of Borrower in
connection with the making of the Loans and has made and shall continue to make
its own appraisal of the creditworthiness of the Borrower. Collateral Agent
shall not have any duty or responsibility either initially or on a continuing
basis to make any such investigation or any such appraisal on behalf of Lenders
or to provide any Lender with any credit or other information with respect
thereto whether coming into its possession before the making of the Loans or any
time or times thereafter and Collateral Agent shall have no responsibility with
respect to the accuracy of or the completeness of the information to Lenders.

      7. Right to Indemnity. Each Lender severally agrees to indemnify
Collateral Agent, (which indemnity shall survive any termination expiration of
the Credit Agreement) to the extent Collateral Agent shall not have been
reimbursed by Borrower, for and against any and all liabilities, obligations,
losses, damages, penalties, actions, judgments, suits, costs, expenses
(including, without limitation, counsel fees and disbursements) or disbursements
of any kind or nature whatsoever which may be imposed on, incurred by or
asserted against Collateral Agent in performing its duties as Collateral Agent
hereunder or in any way relating to or arising out of this Agreement; provided
that no Lender shall be liable for any portion of such liabilities, obligations,
losses, damages, penalties, actions, judgments, suits, costs, expenses or
disbursements which are determined by a court of competent jurisdiction in a
non-appealable proceeding to have resulted solely from Collateral Agent's gross
negligence or willful misconduct. If any indemnity furnished to Collateral Agent
for any purpose shall, in the opinion of Collateral Agent, be insufficient or
become impaired, Collateral Agent may call for additional indemnity and cease,
or not commence, to do the acts indemnified against until such additional
indemnity is furnished.

      8. Cooperation of Lenders. Each Lender shall (a) promptly notify any other
Lender and the Collateral Agent of any failure to pay any amount due hereunder,
under the Original Note or default under the Credit Agreement or known to such
Lender and not reasonably believed to have been previously disclosed to each
other Lender; (b) provide each other Lender and the Collateral Agent with such
information and documentation as such other Lender or the Collateral Agent shall
reasonably request in the performance of their respective duties hereunder,
including all information relative to

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the outstanding balance of principal, interest and other sums owed to such
Lenders by the Borrower; and (c) cooperate with the Collateral Agent with
respect to any and all collection and/or foreclosure procedures at any time
commenced against the Borrower or the Borrower or otherwise in respect of the
Collateral by the Collateral Agent in the name and on behalf of the Lenders

      9. Agency Fee. Borrower and Mobile jointly and severally agree to pay
Collateral Agent an agency fee of $2,600 if one of the events specified in
Section X.3 above is not met by March 16, 2001.

      10. Allocation of Proceeds. The parties acknowledge that Citizens has a
first priority lien on the Collateral, and that Citizens shall be paid in full,
in cash or by wire transfer, all principal, interest, fees and expenses,
including without limitation reasonable attorneys fees, prior to payment to
Mobile of any obligations owing to it by the Borrower. The Collateral Agent is
hereby authorized to liquidate the Collateral under the Collateral Documents at
its sole discretion in accordance with standards equal to the standard of care
it would if it were the sole lender in a lending relationship. Mobile shall have
no right to direct the liquidation of the Collateral until such time as the
Collateral Agent has been repaid in full all obligations under the Retained
Letter of Credit, and all interest, fees and expenses incurred in connection
therewith. The parties acknowledge that Collateral Agent shall have the sole
right to control liquidation of the Collateral and the exercise of any rights
and remedies under the Loan Documents, including, without limitation, control of
the Collateral, direction of enforcement proceedings, commencement and
prosecution of any action to pursue remedies including, without limitation,
foreclosure. The Collateral Agent will use the standard of care in its
administration of its custodial duties hereunder (including, without limitation,
its duties as custodial of the Loan Documents delivered to it by Borrower) equal
to the standard of care it would if it were the sole lender in a lending
relationship.

      11. Additional Collateral Agent Duties. The Collateral Agent (which term,
as used herein, shall include its affiliates and its own and its affiliates'
officers, directors, employees and agents):

            (i) shall have no duties or responsibilities except those expressly
set forth in this Agreement and in the other Loan Documents and shall not, by
reason of this Agreement or any other Loan Document, be a trustee for, or have a
fiduciary relationship in respect of, any Lender;

            (ii) shall not with respect to the Collateral Security under the
Loan Documents, be required to initiate or conduct any litigation or collection
proceedings hereunder or thereunder; and

            (iii) may deem and treat the payee of a Note as the holder thereof
for all purposes hereof unless and until a notice of the assignment or transfer
thereof shall have been filed with the Collateral Agent.

      12. No Action Required. The Collateral Agent shall not be required to take
any action hereunder, under the Loan Documents, or to prosecute or defend any
suit in

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respect of any of the Loan Documents, unless it is indemnified hereunder to its
satisfaction.

      13. Exculpation. NEITHER THE COLLATERAL AGENT NOR ANY OF ITS DIRECTORS,
OFFICERS, EMPLOYEES OR COLLATERAL AGENTS SHALL BE:

            (i) LIABLE TO ANY LENDER FOR ANY ACTION LAWFULLY TAKEN OR OMITTED TO
BE TAKEN BY IT UNDER THIS AGREEMENT OR ANY OTHER LOAN DOCUMENT, OR IN CONNECTION
HEREWITH OR THEREWITH, EXCEPT FOR THE WILLFUL MISCONDUCT OR GROSS NEGLIGENCE OF
THE COLLATERAL AGENT OR ANY OF ITS DIRECTORS, OFFICERS, EMPLOYEES OR COLLATERAL
AGENTS; NOR

            (ii) RESPONSIBLE FOR: ANY RECITALS OR REPRESENTATIONS OR WARRANTIES
HEREIN OR THEREIN; OR APPRAISALS OF CREDIT WORTHINESS OF THE BORROWER OR OF ANY
OTHER OBLIGOR; OR FOR THE EFFECTIVENESS, ENFORCEABILITY, VALIDITY OR DUE
EXECUTION OF THIS AGREEMENT OR ANY OTHER LOAN DOCUMENT; FOR THE CREATION,
PERFECTION OR PRIORITY OF ANY LIENS PURPORTED TO BE CREATED BY ANY OF THE LOAN
DOCUMENTS; OR THE VALIDITY, GENUINENESS, ENFORCEABILITY, EXISTENCE, VALUE OR
SUFFICIENCY OF ANY COLLATERAL SECURITY; NOR

            (iii) RESPONSIBLE TO MAKE ANY INQUIRY RESPECTING THE PERFORMANCE BY
THE BORROWER OF ITS OBLIGATIONS HEREUNDER OR UNDER ANY OTHER LOAN DOCUMENT. ANY
SUCH INQUIRY WHICH MAY BE MADE BY THE COLLATERAL AGENT SHALL NOT OBLIGATE IT TO
MAKE ANY FURTHER INQUIRY OR TO TAKE ANY ACTION.

            THE COLLATERAL AGENT SHALL BE ENTITLED TO RELY UPON ADVICE OF
COUNSEL CONCERNING LEGAL MATTERS AND UPON ANY NOTICE, CONSENT, CERTIFICATE,
STATEMENT OR WRITING WHICH THE COLLATERAL AGENT BELIEVES TO BE GENUINE AND TO
HAVE BEEN PRESENTED BY A PROPER PERSON.

            SHOULD COLLATERAL AGENT OR ITS EMPLOYEES OR COLLATERAL AGENTS
PERFORM ANY ANALYSIS OF BORROWER OR OF ANY OTHER OBLIGOR, AND THEN DELIVER
COPIES OF SAME TO ANY LENDER, EACH LENDER BY ITS EXECUTION HEREOF AGREES THAT IT
SHALL HAVE NO RECOURSE AGAINST COLLATERAL AGENT WITH RESPECT THERETO WITH REGARD
TO ANY ASPECT THEREOF EXCEPT FOR COLLATERAL AGENT'S GROSS NEGLIGENCE WITH REGARD
THERETO.

     14. Successor. The Collateral Agent may resign as such at any time upon at
least 30 days' prior notice to the Borrower and Lenders. If the Collateral Agent
at any time shall resign, the Lenders may appoint another Lender as a successor
Collateral Agent which shall thereupon become the Collateral Agent hereunder. If
the Lenders do not make such appointment within 30 days, the retiring Collateral
Agent may, on behalf of the Lenders, appoint a successor Collateral Agent, which
shall be one of the Lenders

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or, if no Lender shall accept such appointment, a commercial banking institution
organized under the laws of the U.S. (or any State thereof) or a U.S. branch or
agency of a commercial banking institution having a combined capital and surplus
of at least $500,000.000. Upon the acceptance of any appointment as Collateral
Agent hereunder by a successor Collateral Agent, such successor Collateral Agent
shall be entitled to receive from the retiring Collateral Agent such documents
of transfer and assignment as such successor Collateral Agent may reasonably
request, and shall thereupon succeed to and become vested with all rights,
power, privileges and duties of the retiring Collateral Agent, and the retiring
Collateral Agent shall be discharged from its duties and obligations under this
Agreement. After any retiring Collateral Agent's resignation hereunder as the
Collateral Agent, the provisions of this Agreement shall inure to its benefit as
to any actions taken or omitted to be taken by it while it was the Collateral
Agent under this Agreement.

     15. Loans by the Collateral Agent. Citizens shall have the same rights and
powers with respect to the Retained Letter of Credit, as any other Lender and
may exercise the same as if it were not the Collateral Agent. Citizens and its
affiliates may accept deposits from, lend money to, and generally engage in any
kind of business with the Borrower or any Affiliate thereof as if Citizens were
not the Collateral Agent hereunder.

     16. Reliance by Collateral Agent. The Collateral Agent shall be entitled to
rely upon any certification, notice or other communication (including, without
limitation, any thereof by telephone, telecopy, telegram or cable) believed by
it to be genuine and correct and to have been signed or sent by or on behalf of
the proper Person or Persons, and upon advice and statements of legal counsel,
independent accountants and other experts selected by the Collateral Agent. As
to any matters not expressly provided for this by Agreement or any other Loan
Document, the Collateral Agent shall, in all cases, be fully protected in
acting, or in refraining from acting, hereunder or thereunder in accordance with
instructions given by Mobile or all of the Lenders as is required in such
circumstance, and such instructions of such Lenders and any action taken or
failure to act pursuant thereto shall be binding on all of the Lenders.

     17. Defaults. The Collateral Agent shall not be deemed to have knowledge or
notice of the occurrence of a Default unless the Collateral Agent has received
notice from a Lender or the Borrower specifying such Default and stating that
such notice is a "Notice of Default". In the event that the Collateral Agent
receives such a notice of the occurrence of a Default, the Collateral Agent
shall give prompt notice thereof to all Lenders. The Collateral Agent shall
(subject to Section X.3 hereof) take such action with respect to such Default as
shall be directed by Mobile if a default has not occurred under the Retained
Letter of Credit, and Mobile acknowledges that if a default has occurred under
the Retained Letter of Credit then Mobile will defer to any action taken by the
Collateral Agent until the occurrence of the Agency Expiration Date, provided
that, unless and until the Collateral Agent shall have received such directions,
the Collateral Agent may (but shall not be obligated to) take such action, or
refrain from taking such action, with respect to such Default as it shall deem
advisable in the best interest of the Lenders.

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     18. Failure to Act. Except for action expressly required of the Collateral
Agent hereunder and under the Loan Documents, the Collateral Agent shall in all
cases be fully justified in failing or refusing to act hereunder and thereunder
unless it shall receive further assurances to its satisfaction from the Lenders
of their indemnification obligations under Section X.7 hereof against any and
all liability and expense that may be incurred by it by reason taking or
continuing to take any such action.

     19. Consents under Other Loan Documents. The Collateral Agent may, with
prior consent of Mobile (but not otherwise), consent to any modification,
supplement or waiver under any of the Loan Documents, provided that, without the
prior consent of each Lender, the Collateral Agent shall not (except as provided
herein or in the Loan Documents) release any collateral or otherwise terminate
any Lien under Loan Document providing for collateral security, agree to
additional obligations being secured by such collateral security (unless the
Lien for such additional obligations shall be junior to the Lien in favor of the
other obligations secured by such Loan Document), alter the relative priorities
of the obligations entitled to the benefits of the liens created under the Loan
Documents or release any Guarantor from its guarantee obligations under the
Guaranty.

     20. Legal Fees and Expenses. Borrower shall immediately pay any and all of
Citizens' and Mobile's reasonable legal fees and expenses incurred in connection
with the preparation and drafting, negotiation, execution and delivery of the
Fourth Amendment, and in connection with the cash collateral account, if any,
and in connection with the Agency Expiration Date, and with respect to advising
the Collateral Agent of its rights and responsibilities under any of the Loan
Documents, and incurred in connection with the exercise of the Collateral
Agent's, and Citizens', respective rights and remedies under the Loan Documents
and the Retained Letter of Credit. The fees and expenses of counsel to Citizens
incurred with respect to the Fourth Amendment Agreement shall be wire
transferred to counsel to Citizens contemporaneously and on the same day as
Citizen's delivery to Mobile and the Borrower of this Agreement.

     21. Multiple counterparts. This Agreement may be executed in multiple
counterparts, the sum of which will constitute one document.

     [THE BALANCE OF THIS PAGE IS INTENTIONALLY LEFT BLANK]

                                       12
<PAGE>   13
      IN WITNESS WHEREOF, the Lender and the Borrower have caused their duly
authorized officers to execute this Agreement as of the day and year first above
written as an instrument under seal.

WITNESS:                           SHARED TECHNOLOGIES CELLULAR, INC.

                                   By:   /s/ ANTHONY D. AUTORINO
------------------------------          ----------------------------------------
                                            Title: Charman & CEO

                                   MOBILE INVESTMENTS LLC

                                   By:   Oakes Fitzwilliams Executive Death
                                         Benefit & Retirement Scheme (No. 2)
                                         (HLO), Its Member

                                   By:  /s/ HERBERT L. OAKES, JR.
------------------------------          ----------------------------------------
                                         Herbert L. Oakes, Jr.
                                         Trustee

                                   CITIZENS BANK OF MASSACHUSETTS,
                                   FOR ITSELF AND AS COLLATERAL AGENT

                                   By:  /s/ CHRISTOPHER G. DANIEL
------------------------------          ----------------------------------------
                                          Christopher G. Daniel
                                          Its: Vice President

                            CONSENT AND CONFIRMATION

     The undersigned consents to the amendment of the Credit Agreement pursuant
to the Fourth Amendment Agreement, and the terms of the Fourth Amendment
Agreement, and of all underlying documents referred to therein and all documents
entered into pursuant thereto or in connection therewith.

     The undersigned confirms its obligations under that certain Guaranty dated
as of July 7, 1999 (the "Guaranty"), executed by the undersigned, of all
Liabilities (as defined in the Guaranty), as amended hereby, of the Borrower to
the Lender, and confirms its obligations under all documents securing the
Guaranty.

                                       13
<PAGE>   14
     IN WITNESS WHEREOF, the undersigned has caused its duly authorized officer
to execute this Consent and Confirmation as an instrument under Seal.

WITNESS:                                 THE CELLULAR HOTLINE, INC.

                                         By:   /s/ ANTHONY D. AUTORINO
------------------------------                ---------------------------------
                                         Its:  President

                  [NOTARIZATIONS FOR SIGNATURES ON PRIOR PAGE]

STATE OF CONNECTICUT    )
                        )   ss.
COUNTY OF HARTFORD      )

      In Wethersfield on the _______ day of March, 2001, before me personally
appeared the above-named ______________________________________________________,
________________________________________ of SHARED TECHNOLOGIES CELLULAR, INC.
to me known and known by me to be the party executing the foregoing instrument
on behalf of said corporation and acknowledged said instrument so executed to be
his free act and deed in said capacity and the free act and deed of said
corporation.

                                         Notary Public
                                         My Commission Expires:

STATE OF CONNECTICUT    )
                        )  ss.
COUNTY OF HARTFORD      )

      In Wethersfield on the _______ day of March, 2001, before me personally
appeared the above-named ______________________________________________________,
________________________________________ of THE CELLULAR HOTLINE, INC. to me
known and known by me to be the party executing the foregoing instrument on
behalf of said corporation and acknowledged said instrument so executed to be
his free act and deed in said capacity and the free act and deed of said
corporation.

                                         Notary Public
                                         My Commission Expires:

STATE OF CONNECTICUT    )
                        )  ss.
COUNTY OF HARTFORD      )

     In Wethersfield, Connecticut on the ____ day of March, 2001, before me
personally appeared the above-named Herbert Oakes, Jr., the Trustee of Oakes
Fitzwilliams Executive Death Benefit & Retirement Scheme (No. 2) (HLO), member
of Mobile Invest-

                                       14
<PAGE>   15
ments LLC to me known and known by me to be the party executing the foregoing
instrument on behalf of said Lender and acknowledged said instrument so executed
to be his free act and deed in said capacity and the free act and deed of said
Lender.

                                         Notary Public
                                         My Commission Expires:

STATE OF                     )
                             )   ss.
COUNTY OF                    )

     In _____________ on the ___ day of March, 2001, before me personally
appeared the above-named Christopher Daniels, Vice President of Citizens Bank of
Massachusetts to me known and known by me to be the party executing the
foregoing instrument on behalf of said Lender and acknowledged said instrument
so executed to be his free act and deed in said capacity and the free act and
deed of said Lender.

                                         Notary Public
                                         My Commission Expires:

                                       15<PAGE>   1
EXHIBIT 4.21

                               REFERRAL AGREEMENT
                               ------------------

                               REFERRAL AGREEMENT

This Agreement (the "Agreement") is made as of the 28th day of November, 2000,
by and between SHARED TECHNOLOGIES CELLULAR, INC., a Delaware corporation,
having offices at 100 Great Meadow Road, Wethersfield, CT 06109, (the
"Company"), and WILLIAM BOLLES, an individual having a place of business at 26
Broadway, Suite 1615, New York, NY 10004 ("BOLLES").

WHEREAS, BOLLES has provided certain introductions to the Company with respect
to certain prospective licensors ("Licensors"), whose trademark(s) or
tradename(s) ("Marks") may be licensed to the Company in connection with the
Company's prepaid communications products, such as cellular phones and pagers
("Equipment"), and prepaid communications services ("Services"), which such
license agreements ("License Agreements") are identified in Exhibit A hereof;
and

WHEREAS, the Company agrees to compensate BOLLES in connection with each License
Agreement, pursuant to the terms and conditions hereof.

NOW THEREFORE, in consideration of the promises and covenants contained herein,
the receipt and adequacy of which are acknowledged, the parties agree as
follows.

1. BOLLES'S INTRODUCTION TO STC OF LICENSORS. BOLLES has introduced the Company
to certain Licensors whose Marks may be used by the Company in connection with
the marketing and sale of Equipment and Services branded with such Licensors'
Marks. In particular, BOLLES has facilitated discussions between the Company and
Licensors of the Marks "Puff Daddy" Combs ("PDC") and Jennifer Lopez ("Lopez").
In the event that the Company enters into License Agreements for the use of the
PDC and Lopez Marks, then the Company shall Compensate BOLLES in accordance with
Exhibit A hereof. The parties may amend Exhibit A from time to time to add
additional Licensor programs, as the parties may mutually agree.

2. TERM AND TERMINATION. This Agreement shall be effective as of the date hereof
and remain in effect until and for so long as any License Agreement identified
in Exhibit A is in effect. Upon the termination or expiration of the last
surviving License Agreement this Agreement shall automatically terminate without
notice. In the event that the Company does not enter into a License Agreement
for either the PDC or Lopez Mark within six (6) months of the date of this
Agreement, then this Agreement shall be deemed to be null and void as of the
date hereof.

3. COMMISSIONS. STC agrees to pay commissions ("Commissions") to BOLLES during
the term hereof in accordance with Exhibit A attached hereto and made a part
hereof. All Commissions payable by the Company to BOLLES hereunder shall be paid
in arrears, within thirty (30) days after the end of each month in which each
Commission accrues. The Company agrees to provide a report to BOLLES along with
each Commission payment, detailing the basis for such Commission.

4. RELATIONSHIP OF THE PARTIES. BOLLES shall at all times hereunder be deemed to
be an independent contractor of the Company. In no event shall BOLLES's
personnel be considered employees of the Company. Under no circumstances shall
the Company be responsible for workers' compensation premiums, disability
benefits, withholding taxes, social security, unemployment insurance or any
other taxes or benefits with respect to BOLLES or its personnel. BOLLES has no
authority to bind the Company in contract with any third party, including,
without limitation, any Licensor.

5. LIMITATIONS OF LIABILITY. NEITHER PARTY SHALL BE LIABLE TO THE OTHER,
DIRECTLY OR INDIRECTLY, FOR INCIDENTAL, CONSEQUENTIAL (INCLUDING LOST PROFITS),
INDIRECT, PUNITIVE OR SPECIAL DAMAGES ARISING IN ANY WAY OUT OF THIS AGREEMENT.

<PAGE>   2
6. NOTICE. Whenever any notice is required to be given hereunder, such notice
shall be given in writing and personally delivered or sent by certified or
registered mail, return receipt requested, or overnight courier. Notice shall be
deemed to have been given at the time of receipt if personally delivered; three
(3) days after mailing if sent by certified or registered mail; or upon delivery
if sent by overnight courier. All notices shall be sent to the parties'
respective addresses set forth at the beginning of this Agreement. Either party
may change the address at which it is to receive notice by giving notice of the
change to the other party pursuant to this Section.

7. GENERAL.

(a) This Agreement shall be governed by the laws of the State of Connecticut,
without giving effect to any principle of conflict of laws.

(b) This Agreement, including any exhibits and attachments, constitutes the
entire understanding between the parties relating to the subject matter hereof
and supersedes any and all prior discussions, proposals or agreements, whether
oral or written. No modification, addition or waiver to this Agreement shall be
valid unless in writing signed by the parties hereto.

(c) In the event of a dispute arising out of this Agreement, the prevailing
party shall be entitled to recovery of its reasonable legal fees and expenses.

(d) The waiver of any provision of this Agreement shall not be construed as a
continuing waiver of the same or of other provisions hereof.

(e) Any obligation of a party hereto relating to monies owed, as well as those
provisions relating to confidentiality, limitation on liability,
indemnification, noncompetition and any other provisions that by sense and
context are intended to survive performance by either or both parties, shall
survive termination of this Agreement.

(f) The parties acknowledge that they have each read this Agreement in its
entirety, understand it and agree to be bound by the terms and conditions
contained herein.

IN WITNESS WHEREOF, the parties hereto have executed this Agreement by their
duly authorized agents as of the date first written above.

<PAGE>   3
Shared Technologies Cellular, Inc.      William Bolles

By:   /s/ SEAN P. HAYES                 /s/ WILLIAM W. BOLLES
      -----------------------------     -----------------------------------

Its:    Executive Vice President        Date:  November 28, 2000
Date: November 28, 2000

<PAGE>   4
                                    EXHIBIT A

                               COMMISSION SCHEDULE

Subject to the terms and conditions of this Agreement, Commissions payable under
Section 5 of the Agreement will be based on monthly collected revenues received
by the Company from the provision of Services and the sale of Equipment as
follows.

1. "Puff Daddy" Combs and Jennifer Lopez Programs

(a) Equipment Sales. STC agrees to pay to BOLLES monthly Commissions in an
amount equal to $0.25 per unit of Equipment sold with respect to Equipment sold
pursuant to a License Agreement for either the PDC or Lopez Mark.

(b) Usage Sales

      (i) Direct Sales. STC agrees to pay to BOLLES monthly Commissions in an
amount equal to one half (1/2%) of STC's collected monthly revenues from STC's
direct sale of Services through STC's IVR (integrated voice response system) or
its call center, to customers in connection with the use of Equipment sold
pursuant to a License Agreement for either the PDC or Lopez Mark.

      (ii) Sales by Authorized Distributors. STC agrees to pay to BOLLES monthly
Commissions in an amount equal to one-half percent (1/2%) of STC's collected
monthly revenues from the sale by STC and its authorized distributors of usage
cards for Services, which cards are branded with the Mark pursuant to a License
Agreement for either the PDC or Lopez Mark.

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