Document:

<PAGE>

                                                                   Exhibit 10.21

                   AMENDMENT NO. 1 TO SHAREHOLDERS' AGREEMENT

     AMENDMENT NO. 1 TO SHAREHOLDERS' AGREEMENT, dated as of February 2, 2000
(this "Amendment") to that certain Shareholders' Agreement dated as of April 23,
       ---------
1999 between BROADVIEW NETWORKS HOLDINGS, INC. (f/k/a Coaxicom, Inc.), a
Delaware corporation (the "Company"), Baker Communications Fund, L.P. ("Baker"),
                           -------                                      -----
those parties listed on Schedule I to the (i) Series A Preferred Stock Purchase
Agreement, dated as of January 29, 1998, by and among the Company and the Series
A Holders, and (ii) the Series B Preferred Stock Purchase Agreement, dated as of
September 9, 1998, by and among the Company and the Series B Holders, and each
of the individuals listed on the signature pages thereto under the heading
"Founders" (collectively the "Shareholders"), is made by and between the Company
                              ------------
and the Shareholders.

     WHEREAS, Baker desires to assign portions of its option (the "Baker
                                                                   -----
Option") to purchase shares of 8% Series D Convertible Redeemable Preferred
Stock of the Company ("Series D Preferred Stock") to Joel Gross and to certain
                       ------------------------
other parties (together with Joel Gross, the "Assignees"), and the Company and
                                              ---------
the Shareholders desire to approve and consent to such assignment;

     WHEREAS, the Shareholders that hold Series C Convertible Redeemable
Preferred Stock of the Company and the Assignees desire to exercise their
options and purchase, and the Company desires to issue and sell, an aggregate of
6,006,959 shares of Series D Preferred Stock;

     WHEREAS, the Shareholders desire to acknowledge that each Assignee is a
Permitted Transferee of Baker, and waive any and all rights of first offer, tag
along rights and preemptive rights to which they may be entitled under the
Shareholders' Agreement with respect to Baker's assignment of portions of the
Baker Option or the Company's issuance of Series D Preferred Stock; and

     WHEREAS, the Shareholders desire to extend the date by which the Board of
Directors of the Company must be reconstituted under the Shareholders'
Agreement;

     NOW, THEREFORE, in consideration of the premises and mutual covenants and
obligations hereinafter set forth, the Company and the Purchasers hereby agree
as follows:

     SECTION 1.  Definitions.  Capitalized terms used but not otherwise defined
                 -----------
herein shall have the meaning given to them in the Shareholders' Agreement or,
if not defined therein, in the Company's Certificate of Incorporation, as
amended.

     SECTION 2. Amendments to Shareholders' Agreement.  The Shareholders'
                -------------------------------------
Agreement is hereby amended as of the date hereof as follows:
<PAGE>

     (a)  The first sentence is amended and restated in its entirety as follows:

               "THIS SHAREHOLDERS' AGREEMENT (this "Agreement") is made and
          entered into effective as of April 23, 1999 among Broadview Networks
          Holdings, Inc. (f/k/a Coaxicom, Inc.), a Delaware corporation (the
          "Company"), Baker Communications Fund, L.P. ("Baker"), Baker's
          Permitted Transferees who appear as signatories to this Agreement,
          Joel Gross, those parties listed on Schedule I to the (i) Series A
          Preferred Stock Purchase Agreement (the "Series A Holders"), dated as
          of January 29, 1998, by and among the Company and the Series A
          Holders, and (ii) Series B Preferred Stock Purchase Agreement (the
          "Series B Holders"), dated as of September 9, 1998, by and among the
          Company and the Series B Holders (the Series A Holders and the Series
          B Holders are collectively referred to herein as, the "Holders"), and
          each of the individuals listed on the signature pages hereto under the
          heading "Founders" (collectively, the Founders, the Holders, Baker,
          Joel Gross and their respective Permitted Transferees (as defined
          herein) are collectively referred to herein, as the "Stockholders").

     (b)  subsection (iii) of the first recital is amended and restated in its
entirety as follows:

               (iii) the purchase by the Holders of an aggregate of 6,006,959
          shares of 8% Series D Convertible Redeemable Preferred Stock of the
          Company (the "Series D Preferred Shares" and, together with the Series
          C Preferred Shares, the "Priority Preferred Shares"), for an aggregate
          additional purchase price of Twenty Eight Million Dollars
          ($28,000,000);

     (c)  Section 1(a) is amended by substituting "January 31, 2000" for
"December 31, 1999" as the date by which the Board shall be reconstituted to
provide for five (5) members.

     (d)  Section 13 is hereby amended and restated in its entirety as follows:

          13.  Rights Regarding Issuance of Priority Preferred Shares.  Except
               ------------------------------------------------------
               for the purchase by the Series A Holders and Series B Holders of
               Series C Stock and Series D Stock, in each case as provided in
               the Securities Purchase Agreement, as amended, the Stockholders
               hereby waive any other rights they may have to purchase Priority
               Preferred Shares, including, without limitation, any right of
               first offer or preemptive rights with respect to Baker's
               assignment of portions of the Baker Option to its Permitted
               Transferees and to Joel Gross or the Company's issuance of Series
               D
<PAGE>

               Preferred Stock to each of Baker's Permitted Transferees and to
               Joel Gross.

     SECTION 3.  Consent to Assignment by Baker.  The Shareholders hereby
                 ------------------------------
approve and consent to Baker's assignment of its option to purchase 214,534
shares of Series D Preferred Stock to Joel Gross and to Baker's assignment of
its option to purchase 2,038,075 shares of Series D Preferred Stock to the State
Treasurer of the State of Michigan, Custodian of the Michigan Public School
Employees' Retirement System, State Employees' Retirement System and Michigan
State Police Retirement System (the "State of Michigan") on or before February
                                     -----------------
4, 2000, conditional upon the State of Michigan exercising its assigned option
on or before such date.  Baker agrees that any portion of such option that
remains unexercised after such date will be exercised within two business days
by Baker.  The Shareholders acknowledge that, as a result of such approval and
consent, the Assignees are each a Permitted Transferee of Baker and the
provisions of Section 3 and Section 4 of the Shareholders' Agreement are not
applicable to such assignments and transfers by Baker.

     SECTION 4.  Agreement to be Bound by Shareholders' Agreement.  Upon each of
                 ------------------------------------------------
the Assignees' execution of this Amendment, the Shareholders' Agreement shall be
binding upon and inure to the benefit of each of them and their respective
permitted assigns.

     SECTION 5.  Capitalization. The Company hereby represents and warrants to
                 --------------
the Shareholders that the authorized and issued capital stock of the Company
immediately prior to and immediately after the Closing is set forth in Schedule
A attached hereto.

     SECTION 6.  Waiver of Preemptive Rights.  Each Shareholder hereby waives
                 ---------------------------
any preemptive rights to which he or it may be entitled under the Stockholders
Agreement with respect to all issuances of capital stock or other securities by
the Company prior to the date hereof that are reflected in Schedule A.

     SECTION 7.  No Implied Amendments.  Except as herein amended, the
                 ---------------------
Shareholders' Agreement shall remain in full force and effect and is ratified in
all respects.  On and after the effectiveness of this Amendment, each reference
in the Shareholders' Agreement to "this Agreement", "hereunder", "hereof",
"herein" or words of like import, and each reference to the Shareholders'
Agreement in any other agreements, documents or instruments executed and
delivered pursuant to the Securities Purchase Agreement, shall mean and be a
reference to the Shareholders' Agreement, as amended by this Amendment.

     SECTION 8.  Effective Date.  This Amendment shall be effective as of the
                 --------------
date hereof.

     SECTION 9. Counterparts.  This Amendment may be executed by the parties
                ------------
hereto in several counterparts, each of which shall be deemed an original, but
all of which together shall constitute one and the same instrument.

                                       3
<PAGE>

                                 *   *   *   *

                                       4
<PAGE>

   IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first written above.

                              BROADVIEW NETWORKS HOLDING, INC.

                                  /s/ Vern Kennedy
                              By:______________________________
                                      Name:
                                      Title:

                              BAKER COMMUNICATIONS FUND, L.P.

                              By:   Baker Capital Partners, LLC
                                       Its General Partner

                                  /s/ Edward Scott
                              By:______________________________
                                      Name:
                                      Title:

                                   The State Treasurer of the State of Michigan,
                              Custodian of the Michigan Public School
                         Employees' Retirement System, State Employees'
                    Retirement System and Michigan State Police
              Retirement System

                              By:______________________________
                                      Name:
                                      Title:

                              JOEL GROSS

                              ______________________________
<PAGE>

                              COMMUNICATIONS VENTURES II, L.P.

                                  /s/ Roland Van der Meer
                              By:______________________________
                                      Name:
                                      Title:

                              COMMUNICATIONS VENTURES II
                                    AFFILIATES FUND, L.P.

                                  /s/ Roland Van der Meer
                              By:______________________________
                                      Name:
                                      Title:

                              NEW ENTERPRISE ASSOCIATES VII, L.P.

                              By:   NEA Partners VII, L.P.,
                                       General Partner

                                  /s/ Peter Barris
                              By:______________________________
                                      Name:
                                      Title:

                              NEA PRESIDENTS FUND

                                  /s/ Peter Barris
                              By:______________________________
                                      Name:
                                      Title:

                              NEA VENTURES 1998, L.P.

                                  /s/ Peter Barris
                              By:______________________________
                                      Name:
                                      Title:
<PAGE>

                              WPG ENTERPRISE FUND III, L.L.C.

                              By:   WPG VC Fund Adviser, LLC.,
                                       Fund Investment Advisory Member

                              By:______________________________
                                      Name:   Barry Eggers
                                      Title:  Managing Member

                              WEISS, PECK & GREER VENTURE
                                    ASSOCIATES IV, L.L.C.

                              By:   WPG VC Fund Adviser, L.L.C.,
                                       Fund Investment Advisory Member

                              By:________________________________
                                      Name:   Barry Eggers
                                      Title:  Managing Member

                              WPG INFORMATION SCIENCES
                                    ENTREPRENEUR FUND, L.P.

                              By:   WPG VC Fund Adviser, L.L.C.
                                       General Partner

                              By:________________________________
                                      Name:   Barry Eggers
                                      Title:  Managing Member

                              WEISS, PECK & GREER VENTURE
                                    ASSOCIATES IV CAYMAN, L.P.
<PAGE>

                              By:   WPG VC Fund Adviser, L.L.C.,
                                    Fund Investment Advisory Partner

                              By:________________________________
                                      Name:   Barry Eggers
                                      Title:  Managing Member

                              /s/ Vern Kennedy
                              ________________________________
                              Vern M. Kennedy

                              /s/ Terrence Andersom
                              ________________________________
                              Terrence J. Anderson

                              /s/ Philip Smith
                              ________________________________
                              Philip B. Smith

                              /s/ Tracy Korman
                              ________________________________
                              Tracy W. Korman<PAGE>

                                                                   EXHIBIT 10.22

                  AMENDMENT NO. 2 TO SHAREHOLDERS' AGREEMENT

     AMENDMENT NO. 2 TO SHAREHOLDERS' AGREEMENT, dated as of February 4, 2000
(this "Amendment") to that certain Shareholders' Agreement dated as of April 23,
       ---------
1999, as amended by Amendment No. 1 dated February 2, 2000 ("Amendment No. 1"),
                                                             ---------------
between BROADVIEW NETWORKS HOLDINGS, INC. (f/k/a Coaxicom, Inc.), a Delaware
corporation (the "Company"), Baker Communications Fund, L.P. ("Baker"), Joel
                  -------                                      -----
Gross, those parties listed on Schedule I to the (i) Series A Preferred Stock
Purchase Agreement, dated as of January 29, 1998, by and among the Company and
the Series A Holders, and (ii) the Series B Preferred Stock Purchase Agreement,
dated as of September 9, 1998, by and among the Company and the Series B
Holders, and each of the individuals listed on the signature pages thereto under
the heading "Founders", is made by and between the Company the other parties who
appear as signatories to this Amendment (collectively, the "Shareholders").
                                                            ------------

     WHEREAS, Section 3 of Amendment No. 1 contemplated Baker assigning the
remainder of its option (the "Baker Option") to purchase shares of 8% Series D
                              ------------
Convertible Redeemable Preferred Stock of the Company ("Series D Preferred
                                                        ------------------
Stock") to the State Treasurer of the State of Michigan, as Custodian of the
Michigan Public School Employees' Retirement System, State Employees' Retirement
System and Michigan State Police Retirement System (the "State of Michigan
                                                         -----------------
Retirement Systems") on or before February 4, 2000, conditional upon the State
------------------
of Michigan Retirement Systems exercising their assigned option on or before
such date.

     WHEREAS, Baker now desires to assign the remainder of its option to the
State of Michigan Retirement Systems, and the State of Michigan Retirement
Systems desire to exercise their assigned option as of the date hereof, subject
to the terms of this Amendment, and the Company and the Purchasers desire to
approve and consent to such exercise; and

     WHEREAS, the Shareholders have previously acknowledged that the State of
Michigan Retirement Systems are collectively a Permitted Transferee of Baker,
and waived any and all rights of first offer, tag along rights and preemptive
rights to which they may have been entitled under the Shareholders' Agreement
with respect to Baker's assignment of portions of the Baker Option or the
Company's issuance of Series D Preferred Stock; and

     NOW, THEREFORE, in consideration of the premises and mutual covenants and
obligations hereinafter set forth, the Company and the Purchasers hereby agree
as follows:

     SECTION 1.  Definitions.  Capitalized terms used but not otherwise defined
                 -----------
herein shall have the meaning given to them in the Shareholders' Agreement or,
if not defined therein, in the Company's Certificate of Incorporation, as
amended.

     SECTION 2. Amendments to Shareholders' Agreement.  The Shareholders'
                -------------------------------------
Agreement is hereby amended as of the date hereof as follows:

     (a)  The first sentence is amended and restated in its entirety as follows:
<PAGE>

               "THIS SHAREHOLDERS' AGREEMENT (this "Agreement") is made and
          entered into effective as of April 23, 1999 among Broadview Networks
          Holdings, Inc. (f/k/a Coaxicom, Inc.), a Delaware corporation (the
          "Company"), Baker Communications Fund, L.P. ("Baker"), the State
          Treasurer of the State of Michigan, as Custodian of the Michigan
          Public School Employees' Retirement System, State Employees'
          Retirement System and Michigan State Police Retirement System (the
          "State of Michigan Retirement Systems"), Joel Gross, those parties
          listed on Schedule I to the (i) Series A Preferred Stock Purchase
          Agreement (the "Series A Holders"), dated as of January 29, 1998, by
          and among the Company and the Series A Holders, and (ii) Series B
          Preferred Stock Purchase Agreement (the "Series B Holders"), dated as
          of September 9, 1998, by and among the Company and the Series B
          Holders (the Series A Holders and the Series B Holders are
          collectively referred to herein as, the "Holders"), and each of the
          individuals listed on the signature pages hereto under the heading
          "Founders" (collectively, the Founders, the Holders, Baker, the State
          of Michigan Retirement Systems, Joel Gross and their respective
          Permitted Transferees (as defined herein) are collectively referred to
          herein, as the "Stockholders").

     (b)  Section 26(a) is hereby amended and restated in its entirety as
          -------------
follows:

               (a) To the fullest extent permitted by applicable law and public
          policy, the parties hereby irrevocably submit to the non-exclusive
          jurisdiction of any federal or state court located within the Borough
          of Manhattan, State of New York over any dispute arising or relating
          to this Agreement or any of the transactions contemplated hereby and
          each party hereby irrevocably agrees that all claims in respect of
          such dispute or any suit, action or proceeding related thereto may be
          heard and determined in such courts.  The parties hereby irrevocably
          waive, to the fullest extent permitted by applicable law and public
          policy, any objection which they may now or hereafter have to the
          laying of venue of any such dispute brought in such court or any
          defense of inconvenient forum for the maintenance of such dispute.
          Each of the parties hereto agrees that a judgment in any such dispute
          may be enforced in other jurisdictions by suit on the judgment or in
          any other manner provided by law.

     SECTION 3.  Agreement to be Bound by Shareholders' Agreement.  Upon the
                 ------------------------------------------------
State of Michigan Retirement Systems' execution of this Amendment, the
Shareholders' Agreement shall be binding upon and inure to the benefit of the
State of Michigan Retirement Systems and their permitted assigns.

     SECTION 4.  Capitalization. The Company hereby represents and warrants to
                 --------------
the Shareholders that the authorized and issued capital stock of the Company
immediately prior to and immediately after the February 2, 2000 and February 4,
2000 closings of the sale of shares of Series D Preferred Stock is set forth in
Schedule A attached hereto.

                                       2
<PAGE>

     SECTION 5.  Waiver of Preemptive Rights.  Each Shareholder hereby waives
                 ---------------------------
any  preemptive rights to which he or it may be entitled under the Stockholders
Agreement with respect to all issuances of capital stock or other securities by
the Company prior to the date hereof that are reflected in Schedule A.

     SECTION 6.  No Implied Amendments.  Except as herein amended, the
                 ---------------------
Shareholders' Agreement shall remain in full force and effect and is ratified in
all respects.  On and after the effectiveness of this Amendment, each reference
in the Shareholders' Agreement to "this Agreement", "hereunder", "hereof",
"herein" or words of like import, and each reference to the Shareholders'
Agreement in any other agreements, documents or instruments executed and
delivered pursuant to the Securities Purchase Agreement, shall mean and be a
reference to the Shareholders' Agreement, as amended by this Amendment.

     SECTION 7.  Effective Date.  This Amendment shall be effective as of the
                 --------------
date hereof.

     SECTION 8. Counterparts.  This Amendment may be executed by the parties
                ------------
hereto in several counterparts, each of which shall be deemed an original, but
all of which together shall constitute one and the same instrument.

                                 *   *   *   *

                                       3
<PAGE>

     IN WITNESS WHEREOF, the parties have executed this Amendment as of the date
first written above.

                              BROADVIEW NETWORKS HOLDING, INC.

                              By:    /s/ Vern M. Kennedy
                                 ------------------------------
                                  Name:  Vern M. Kennedy
                                  Title: President and CEO

                              BAKER COMMUNICATIONS FUND, L.P.

                              By:  Baker Capital Partners, LLC
                                     Its General Partner

                              By:    /s/ Edward Scott
                                 ------------------------------
                                  Name:  Edward Scott
                                  Title: General Partner

                              The State Treasurer of the State of Michigan, as
                              Custodian of the Michigan Public School Employees'
                              Retirement System, State Employees' Retirement
                              System and Michigan State Police Retirement System

                              By:    /s/ David C. Turner
                                 ------------------------------
                                  Name:  David C. Turner
                                  Title: Administrator, Alternative
                                         Investments Division

                              JOEL GROSS

                              /s/ Joel Gross
                              ------------------------------
<PAGE>

                              COMMUNICATIONS VENTURES II, L.P.
                              By its General Partner ComVenII, LLC

                              By:    /s/ Roland A. Van der Meer
                                 ------------------------------
                                  Name:  Roland A. Van der Meer
                                  Title: Member

                              COMMUNICATIONS VENTURES II
                                    AFFILIATES FUND, L.P.

                              By:    /s/ Roland A. Van der Meer
                                 ------------------------------
                                  Name:  Roland A. Van der Meer
                                  Title: Member

                              NEW ENTERPRISE ASSOCIATES VII, L.P.

                              By:  NEA Partners VII, L.P.,
                                     General Partner

                              By:    /s/ Peter Barris
                                 ------------------------------
                                  Name:
                                  Title:

                              NEA PRESIDENTS FUND

                              By:    /s/ Peter Barris
                                 ------------------------------
                                  Name:
                                  Title:

                              NEA VENTURES 1998, L.P.

                              By:    /s/ Peter Barris
                                 ------------------------------
                                  Name:
                                  Title:
<PAGE>

                              WPG ENTERPRISE FUND III, L.L.C.

                              By:  WPG VC Fund Adviser, LLC.,
                                     Fund Investment Advisory Member

                              By:    /s/ Barry Eggers
                                 ------------------------------
                                  Name:  Barry Eggers
                                  Title:  Managing Member

                              WEISS, PECK & GREER VENTURE
                                    ASSOCIATES IV, L.L.C.

                              By:  WPG VC Fund Adviser, L.L.C.,
                                     Fund Investment Advisory Member

                              By:    /s/ Barry Eggers
                                 ------------------------------
                                  Name:  Barry Eggers
                                  Title:  Managing Member

                              WPG INFORMATION SCIENCES
                                    ENTREPRENEUR FUND, L.P.

                              By:  WPG VC Fund Adviser, L.L.C.
                                     General Partner

                              By:    /s/ Barry Eggers
                                 ------------------------------
                                  Name:  Barry Eggers
                                  Title:  Managing Member

                              WEISS, PECK & GREER VENTURE
                                    ASSOCIATES IV CAYMAN, L.P.

                              By:  WPG VC Fund Adviser, L.L.C.,
                                    Fund Investment Advisory Partner

                              By:    /s/ Barry Eggers
                                 ------------------------------
                                  Name:  Barry Eggers
                                  Title:  Managing Member
<PAGE>

                              /s/ Vern M. Kennedy
                              --------------------------------
                              Vern M. Kennedy

                              /s/ Terrence J. Anderson
                              --------------------------------
                              Terrence J. Anderson

                              /s/ Philip B. Smith
                              --------------------------------
                              Philip B. Smith

                              /s/ Tracy W. Korman
                              --------------------------------
                              Tracy W. Korman

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