<PAGE>   1
                                                                     Exhibit 4.2


                            FIFTH AMENDMENT AGREEMENT

     THIS FIFTH AMENDMENT AGREEMENT (the "Agreement") is entered as of March 30,
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" or "Lender").

RECITALS:

     On July 7, 1999, State Street Bank and Trust Company ("State Street") 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, that certain Third Amendment Agreement dated
August 8, 2000, and that certain Fourth Amendment Agreement dated March 1, 2001
(referred to herein collectively as the "Credit Agreement"). State Street
assigned its interest in the Credit Agreement, the loans made thereunder, and
the documents executed in connection therewith to Citizens Bank of Massachusetts
("Citizens"), pursuant to which Citizens extended to the Borrower a Revolving
Credit Facility.

      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.
Anthony Autorino assigned the Loan to Mobile pursuant to a certain Nonrecourse
Assignment and Acceptance agreement dated March 14, 2001.

     Pursuant to said Fourth Amendment Agreement, Citizens 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 thereof. As of March 29, 2001 Citizens
has resigned as Collateral Agent and has assigned all of its interests in the
Credit Agreement and the collateral pledged thereby to Mobile.

     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:


                                       1
<PAGE>   2
SECTION I.  AMENDMENTS TO CREDIT AGREEMENT.

     The Credit Agreement is amended hereby as follows:

     1.   All references to the Collateral Agent are hereby deleted, and the
parties acknowledge that Mobile has succeeded to the interests of Citizens, for
itself and as Agent, under the Credit Agreement.

     2.   All references to the "Lender," the "Secured Party" or the "Assignee"
under the Credit Agreement and the Loan Documents shall be deemed amended hereby
to refer solely to Mobile.

     3.   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.

     4.   Notwithstanding the terms of the Fourth Amendment Agreement, Mobile
shall make an Advance of $1,000,000 on the date hereof.

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

               "Fifth Amendment Agreement" shall mean that certain Fifth
          Amendment Agreement entered into between the Borrower and the Lender
          dated as of March 30, 2001."

     6.   The following is added as Section 7.1(p) of the Credit Agreement:

          (p) If the Borrower fails to obtain the shareholder approval described
          in the letter agreement attached as Exhibit C to the Fifth Amendment
          Agreement at the next meeting of the shareholders of the Borrower.

     7.   The date " August 31, 2001" in the definition of the "Commitment
Termination Date" is hereby changed to "September 30, 2001."

     8.   Section X of the Fourth Amendment Agreement is deleted.

SECTION II.  AMENDMENT TO THE ORIGINAL NOTE.

     The Original Note is amended to extend the maturity date thereof to
September 30, 2001.

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
<PAGE>   3
     2.   Borrower represents and agrees that, in addition to the amounts
advanced in Section I.2. above, there is currently outstanding the principal
amount of $628,006.96 under the Credit Agreement and Original Note (but not
including the advance made hereunder), together with accrued interest thereon
from March 31, 2001 ($111.23 per diem), legal fees and accounting fees of
$25,000, 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.

SECTION IV.  RESERVATION OF RIGHTS.

     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 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, and the other documents executed
     in connection herewith, there are no other understandings, express or
     implied between Mobile 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:

          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 or any of Mobile's 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 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 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.


                                       3
<PAGE>   4
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 Mobile'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
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).



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 Agreement and the Amendment to Note, as
incorporated therein by reference; and


                                       4
<PAGE>   5
          b)   except as specifically amended hereby and by all other documents
executed in connection herewith, 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 and by such other
documents executed in connection herewith, shall continue to secure the
Borrower's obligations under the Credit Agreement, the Original Note as amended,
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.

SECTION X.  MOBILE REPRESENTATIONS.

     Mobile represents that (a) each of its members has been advised and
understands that the Loan and Warrants (and shares of Common Stock issuable upon
exercise thereof) have not been registered under the Securities Act of 1933, as
amended (the "Act"), on the basis that no distribution or public offering of the
Loan and Warrants (and share of Common Stock issuable upon exercise thereof) is
to be effected, except in compliance with applicable securities laws and
regulations or pursuant to an exemption therefrom, and that in this connection,
the Borrower is relying in part on the representations of Mobile set forth
herein; (b) each of its Members is purchasing the Loan and Warrants (and shares
of Common Stock issuable upon exercise thereof) for investment purposes, for its
own account and not with a view to, or for sale in connection with, any
distribution thereof in violation of Federal or state securities laws; (c) each
of its Members is an "accredited investor" within the meaning of Rule 501(a) of
Regulation D under the Act and, by reason of its business or financial
experience, such Member has the capacity to protect its own interest in
connection with the transactions contemplated hereunder.


                                       5
<PAGE>   6
             [THE BALANCE OF THIS PAGE IS INTENTIONALLY LEFT BLANK]


                                       6
<PAGE>   7
      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.


/s/ J. Rieber                      By: /s/ Anthony D. Autorino
-------------                          -----------------------
                                       Title: Chairman and CEO

                                   MOBILE INVESTMENTS LLC

                                   By:   Oakes, Fitzwilliams & Co., Inc.
                                         Its Manager


/s/ Parveen Abbas                  By: /s/ Herbert L. Oakes, Jr.
-----------------                      -------------------------
                                       Herbert L. Oakes, Jr.
                                       Its President



                            CONSENT AND CONFIRMATION

     The undersigned consents to the amendment of the Credit Agreement pursuant
to the Fifth Amendment Agreement, and the terms of the Fifth 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.

     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.


/s/ J. Rieber                            By: /s/ Anthony D. Autorino
-------------                                -----------------------
                                         Its: President


                                       7
<PAGE>   8
                  [NOTARIZATIONS FOR SIGNATURES ON PRIOR PAGE]

STATE OF CONNECTICUT    )
                        )   ss. Wethersfield
COUNTY OF HARTFORD      )

     In Wethersfield on the 29th day of March, 2001, before me personally
appeared the above-named Anthony D. Autorino, Chairman and CEO 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.

                                         /s/ Mary Lynn Carney
                                         --------------------
                                         Notary Public
                                         My Commission Expires: March 31, 2004



STATE OF   CONNECTICUT  )
                        )  ss. Wethersfield
COUNTY OF HARTFORD      )

     In Wethersfield on the 29th day of March, 2001, before me personally
appeared the above-named Anthony D. Autorino, President 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.

                                         /s/ Mary Lynn Carney
                                         --------------------
                                         Notary Public
                                         My Commission Expires: March 31, 2004


                                       8
<PAGE>   9
STATE OF                )
                        )  ss.
COUNTY OF               )

     In London on the 29th day of March, 2001, before me personally appeared the
above-named Herbert Oakes, Jr., the President of Oakes, Fitzwilliams & Co.,
Inc., Manager of Mobile Investments 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.



                                         /s/ Parveen Abbas
                                         -----------------
                                         Notary Public
                                         My Commission Expires:


                                       9