<PAGE>   1
                                                                     Exhibit 4.2


                           SECOND AMENDMENT AGREEMENT

         THIS SECOND AMENDMENT AGREEMENT (the "Agreement") is entered as of May
1, 2000 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 CITIZENS BANK OF
MASSACHUSETTS, a Massachusetts Bank, having an office and place of business at
28 State Street, Boston, MA 02109 (the "Bank").

                                    RECITALS:

         On July 7, 1999, the Bank and the Borrower entered into a Loan
Agreement, as amended by that certain First Amendment Agreement dated as of
December 3, 1999 (referred to herein collectively as the "Credit Agreement")
pursuant to which the Bank extended to the Borrower a Revolving Credit Facility
which is presently existing in the maximum aggregate line availability of
$10,000,000.00. The Borrower has executed and delivered to the Bank on July 7,
1999 a Secured Revolving Credit Promissory Note in the original principal amount
of Ten Million Dollars ($10,000,000.00) (the "Original Note").

         The Borrower and the Bank have agreed to amend the Credit Agreement
upon the terms and conditions set forth herein.

         NOW, THEREFORE, in consideration of the provisions herein contained,
Borrower and the Bank, 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.       SECTION 1.1 OF THE CREDIT AGREEMENT IS AMENDED BY AMENDING AND
RESTATING IN ITS ENTIRETY THE DEFINITION OF "REVOLVING CREDIT COMMITMENT" AS
FOLLOWS:

         ""Revolving Credit Commitment" shall mean Five Million Dollars
         ($5,000,000.00)."
<PAGE>   2
         2.       SECTION 5.6 OF THE CREDIT AGREEMENT IS AMENDED AND RESTATED IN
ITS ENTIRETY AS FOLLOWS:

                  "5.6 Minimum Prepaid Lines. Maintain Minimum Prepaid Lines
                  commencing May 1, 2000, as follows, to be tested as follows:

<TABLE>
<CAPTION>
                  Time Period                  Minimum Prepaid Lines
                  -----------                  ---------------------
<S>                                            <C>
                  as of April 28, 2000         115,000

                  as of May 31, 2000           130,000

                  as of June 30, 2000          145,000
</TABLE>

                  as of the last day of each Fiscal Quarter after June 30, 2000,
                  the Borrower shall increase its Minimum Prepaid Lines by
                  25,000 over the amount of Minimum Prepaid Lines for the prior
                  Fiscal Quarter."

         3.       SECTION 5.8 OF THE CREDIT AGREEMENT IS AMENDED AND RESTATED IN
ITS ENTIRETY AS FOLLOWS:

                  "5.8 Maximum Net Loss/Minimum Net Income. Maintain Maximum Net
                  Loss/Minimum Net Income for each Fiscal Quarter, commencing
                  with the Fiscal Quarter ending March 30, 2000, as follows, to
                  be tested quarterly:

<TABLE>
<CAPTION>
                  Time Period                                        Minimum Net Income
                  -----------                                        ------------------
<S>                                                           <C>
                  Fiscal Quarter ending March 30, 2000        ($4,500,000.00) Maximum Net Loss

                  Fiscal Quarter ending June 30, 2000         ($3,000,000.00) Maximum Net Loss

                  Fiscal Quarter ending September 30, 2000    ($500,000.00) Maximum Net Loss

                  Each Fiscal Quarter thereafter              + $500,000.00 Minimum Net Income"

</TABLE>



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         4.       SECTION 5.10 OF THE CREDIT AGREEMENT IS AMENDED AND RESTATED
IN ITS ENTIRETY AS FOLLOWS:

                  "5.10 Minimum Total Stockholder's Equity. Maintain for each
                  fiscal quarter commencing with the quarter ending March 30,
                  2000, a Minimum Total Stockholder's Equity as follows, to be
                  tested quarterly:

<TABLE>
<CAPTION>
                  Time Period                                    Minimum Total Stockholder's Equity
                  -----------                                    ----------------------------------
<S>                                                              <C>
                  Fiscal Quarter ending March 30, 2000           ($6,200,000.00)

                  Fiscal Quarter ending June 30, 2000            ($2,000,000.00)

                  Fiscal Quarter Ending September 30, 2000       ($2,500,000.00)

</TABLE>

                  as of the last day of each Fiscal Quarter after September 30,
                  2000, the Borrower shall increase its Minimum Total
                  Stockholder's Equity by $500,000.00 over the amount of Minimum
                  Total Stockholders's Equity for the prior Fiscal Quarter."

         5.       THE CREDIT AGREEMENT IS FURTHER AMENDED BY ADDING A NEW
SECTION 5.22 THERETO AS FOLLOWS:

                  "5.22 Minimum Additional Capital. The Borrower shall have
                  raised from the date hereof through June 30, 2000 a minimum
                  additional capital and equity contribution of Seven Million
                  Five Hundred Thousand Dollars ($7,500,000.00), provided
                  however that evidence thereof to be received by the Bank on or
                  before June 30, 2000 shall consist of the following:

                  a)       a written agreement by the equity contributor
                           outlining the terms and conditions of said
                           contribution; and

                  b)       evidence delivered to the Bank reasonably
                           satisfactory to it in its sole discretion as to the
                           financial substance and resources of said equity
                           contributor; and

                  c)       any and all conditions and contingencies for said
                           equity contribution shall be reasonably satisfactory
                           to the Bank in its sole discretion; and

                  d)       the date by which said contingency shall have
                           satisfied and said funds shall have been contributed
                           to the Bank shall reasonably acceptable to the Bank
                           in its sole discretion."


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<PAGE>   4
SECTION II. AMENDMENT TO THE ORIGINAL NOTE.

         The Original Note is amended and restated in its entirety by the
Borrower's execution and delivery to the Bank of that certain Amended and
Restated Revolving Credit Promissory Note in the original principal amount of
Five Million Dollars ($5,000,000.00) a form of which is attached hereto as
Exhibit A, with all blanks completed, and duly executed by the Borrower
(referred to herein as the "Successor Note").

SECTION III. CONDITIONS.

         A.       CONDITION PRECEDENT - DELIVERY OF DOCUMENTS.

                  The Bank shall have no obligation to make advances under the
Credit Agreement unless the following conditions are satisfied or waived by the
Bank:

                  1.       The Borrower has delivered to the Bank the following
         documents in form and substance satisfactory to the Bank, the receipt
         of which is hereby acknowledged (the "Amendment Documents"):

                           a)       the Successor Note, duly executed by the
                                    Borrower;

                           b)       Certificate of No Default from the Borrower,
                                    duly executed by the Borrower;

                           c)       Corporate Borrowing Authorization and
                                    Certificate of Incumbency of Officers and
                                    Directors - the Borrower;

                           d)       Corporate Guaranty Authorization and
                                    Certificate of Incumbency of Officers and
                                    Directors and Identification of Shareholders
                                    - The Cellular Hotline, Inc.; and

                           e)       a Fifteen Thousand Dollar ($15,000.00) fee,
                                    payable on even date, for the Waiver by the
                                    Bank dated March 28, 2000 of certain loan
                                    covenant defaults; and

                           f)       the delivery of such other documents
                                    reflected in that certain Closing Agenda
                                    attached hereto as Exhibit A and
                                    incorporated herein by reference, as may be
                                    reasonably required by the Bank in
                                    connection with the transaction contemplated
                                    hereby.

                  2.       All legal matters incident to this Agreement and the
         transactions contemplated hereby shall be satisfactory to the Bank and
         its counsel.

         B.       RECONFIRMATION OF COVENANTS, REPRESENTATIVES AND WARRANTIES.


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<PAGE>   5
                  1.       The Borrower further reaffirms all of its
obligations, as amended hereby, under the Credit Agreement, and under the
Security Documents.

                  2.       The Borrower acknowledges that upon its delivery to
the Bank of the duly executed Amendment Documents, that all representations,
warranties and covenants set forth in the Credit Agreement are deemed to be made
again as of the date of the delivery hereof, and that the Borrower does not have
any information contrary to (a) any of the conclusions reflected in that certain
set of projections prepared by Borrower and delivered to Lender; or (b) any of
the assumptions or premises upon which said projections were based.

         C.       RESERVATION OF RIGHTS.

                  The Bank and the Borrower agree that:

                           a) 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;

                           b) Notwithstanding the terms hereof: the Bank 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;

                           c) There are no other understandings, express or
         implied between the Bank and the Borrower regarding the Credit
         Agreement and the Original Note; and d) Notwithstanding any prior
         course of practice or conduct, the Borrower acknowledges that the Bank
         has not waived, and has no obligation to waive, any subsequent Events
         of Default under the Credit Agreement and the Original Note, or under
         this Agreement.

         D.       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 the Bank or
any of the Bank's rights with respect to such liabilities; and

                           2) be in all respects ratified and affirmed.


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<PAGE>   6
                  Notwithstanding the foregoing, any amendments of the Credit
Agreement and the Original Note to which the parties hereto have agreed
previously and which are not incorporated herein by reference or otherwise,
shall be deemed of no further force and effect upon the execution hereof.

                  2.       The Borrower acknowledges that all of the liabilities
and obligations of the Borrower to the Lender now existing and hereafter
incurred are secured by the security described in the Security Documents defined
in the Credit Agreement and by the security described in the Amendment
Documents; the Borrower further acknowledges that the Bank 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 the
Bank.

         E.       GENERAL.

                  1.       CONSTRUCTION Incorporated herein by reference are the
representations, warranties, agreements, affirmative and negative, definitions,
terms and conditions all as set forth in (i) the Credit Agreement and the
Original Note and all documents executed in connection therewith or pursuant
thereto and (ii) the Amendment Documents. This Agreement and the Credit
Agreement and the Original Note, and the Amendment 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 and the Amendment Documents.

                  2.       GOVERNING LAW. This Agreement, the Successor Note,
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).


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<PAGE>   7
                  3.       SECURITY DOCUMENTS. The Borrower and The Cellular
Hotline, Inc., 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, and
         all indebtedness incurred pursuant thereto 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 Bank or
         any of the Bank'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 and all other obligations of the Borrower and of The Cellular
         Hotline, Inc. to the Bank, whether now existing or hereafter arising.

                  3.       WAIVER OF TRIAL BY JURY. BORROWER AND BANK 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 BANK TO ACCEPT THIS AGREEMENT AND TO AMEND
THE REVOLVING CREDIT FACILITY.

         IN WITNESS WHEREOF, the Bank 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/ Vincent DiVincenzo
                                         Title: CFO

                      SIGNATURES CONTINUED ON THE NEXT PAGE


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<PAGE>   8
                    SIGNATURES CONTINUED FROM THE PRIOR PAGE

                                      CITIZENS BANK OF MASSACHUSETTS



________________________________      By:/s/ Michael S. St. Jean
                                          Michael S. St.Jean
                                          Title: Vice President

                            CONSENT AND CONFIRMATION

         The undersigned consents to the amendment of the Credit Agreement
pursuant to the Second Amendment Agreement, and the terms of the Second
Amendment Agreement, including but not limited to Section III. E. 3. thereof,
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 Bank, 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 of the ____ day of April,
2000.

WITNESS:                              THE CELLULAR HOTLINE, INC.


________________________________      By:________________________________
                                        Its:

STATE OF CONNECTICUT
COUNTY OF HARTFORD

         In Whethersfield on the ______ day of April, 2000, 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:


                      NOTARIZATIONS CONTINUED ON NEXT PAGE



                                      -8-
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                     NOTARIZATIONS CONTINUED FROM PRIOR PAGE

STATE OF CONNECTICUT
COUNTY OF HARTFORD

         In Whethersfield on the ______ day of April , 2000, 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 MASSACHUSETTS
COUNTY OF SUFFOLK

         In Boston on the ______ day of April, 2000, before me personally
appeared the above-named Michael S. St. Jean, Vice President of CITIZENS BANK OF
MASSACHUSETTS, of Boston, Massachusetts to me known and known by me to be the
party executing the foregoing instrument on behalf of said Massachusetts Bank
and acknowledged said instrument so executed to be his free act and deed in said
capacity and the free act and deed of said Massachusetts Bank.



                                        __________________________________
                                        Notary Public
                                        My Commission Expires:


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