| Principal Shareholders PRINCIPAL STOCKHOLDERS
 
 The following table sets forth as of March 8, 2000 and as adjusted to give
 effect to the sale of common stock offered hereby, certain information regarding
 beneficial ownership of our common stock by:
 
 - each person who is known to us to be the beneficial owner of more than 5%
 of the outstanding shares of our common stock;
 - each director;
 - each executive officer named in the "Summary Compensation Table"; and
 - all directors and executive officers as a group.
 
 The amounts and percentage of common stock beneficially owned are reported
 on the basis of regulations of the SEC governing the determination of beneficial
 ownership of securities. Under the rules of the SEC, a person is deemed to be a
 "beneficial owner" of a security if that person has or shares "voting power,"
 which includes the power to vote or to direct the voting of such security, or
 "investment power," which includes the power to dispose of or direct the
 disposition of such security. A person is also deemed to be a beneficial owner
 of any securities of which that person has a right to acquire beneficial
 ownership within 60 days. All persons listed have sole voting and investment
 power with respect to their shares unless otherwise indicated.
 
 SHARES BENEFICIALLY OWNED (1)
 --------------------------------------
 PERCENTAGE    PERCENTAGE
 OWNED         OWNED
 NAME AND BUSINESS ADDRESS OF             NUMBER OF    BEFORE THE      AFTER
 BENEFICIAL OWNER                           SHARES      OFFERING    THE OFFERING
 ----------------------------             ----------   ----------   ------------
 PRINCIPAL STOCKHOLDERS
 ComVentures (2)........................   3,679,228      12.16%
 505 Hamilton Avenue, Suite 305
 Palo Alto, CA 94301
 Bedrock Capital Partners I, L.P. (3)...   3,649,946      12.13%
 One Boston Place, Suite 3310
 Boston, MA 02108
 CB Capital Investors, L.P..............   3,157,111      10.51%
 380 Madison Avenue, 12th Floor
 New York, NY 10017
 JP Morgan Investment Corporation (4)...   3,157,111      10.51%
 60 Wall Street
 New York, NY 10260
 Internet Capital Group, Inc. (5).......   2,389,721       7.94%
 800 The Safeguard Building
 435 Devon Park Drive
 Wayne, PA 19087
 BancBoston Ventures, Inc...............   2,057,798       6.85%
 175 Federal Street, 10th Floor
 Boston, MA 02110
 DIRECTORS AND EXECUTIVE OFFICERS
 Anthony L. Craig (6) (7)...............   1,747,636       5.82%
 Alex Mashinsky (7).....................   6,752,209      22.49%
 Robert S. Vaters (7) (8)...............      43,750          *
 Neil A. Torpey (7) (9).................      28,730          *
 Norris M. Hall, III (7) (10)...........      20,833          *
 Douglas A. Alexander (11)..............   2,389,721       7.94%
 Philip Summe (12)......................   3,157,111      10.51%
 Paul G. Theunissen (13)................   3,157,111      10.51%
 Roland A. Van der Meer (14)............   3,679,228      12.16%
 All directors and executive
 officers as a group
 (nine persons) (15)..................  20,976,329      69.37%
 
 ------------------------
 *   Less than 1%.
 
 (1) Calculated according to Rule 13d-3(d) of the Securities Exchange Act of
 1934. Under Rule 13d-3(d), shares not outstanding that are subject to
 options, warrants, rights or conversion privileges exercisable within
 60 days are deemed outstanding for the purpose of calculating the number and
 percentage owned by the holder of the options, warrants, rights or
 conversion privileges. However, these shares are not deemed outstanding for
 the purpose of calculating the percentage owned by any other person listed.
 As of March 1, 2000, we had 10,800,952 shares of common stock outstanding.
 
 (2) Includes 3,446,161 shares of common stock and warrants to purchase 56,208
 shares of common stock owned by Communications Ventures III, L.P. and
 174,049 shares of common stock and warrants to purchase 2,810 shares of
 common stock which are owned by Communications Ventures III CEO &
 Entrepreneurs' Fund, L.P.
 
 (3) Includes 3,334,859 shares of common stock and warrants to purchase 54,810
 shares of common stock owned by Bedrock Capital Partners I, L.P., 116,346
 shares of common stock and warrants to purchase 1,912 shares of common stock
 owned by VBW Employee Bedrock Fund, L.P. and 139,723 shares of common stock
 and warrants to purchase 2,296 shares of common stock owned by Credit Suisse
 First Boston Bedrock Fund, L.P.
 
 (4) Includes 2,810,465 shares of common stock owned by JP Morgan Investment
 Corporation and 346,646 shares of common stock which are owned by Sixty Wall
 Street SBIC Fund, L.P.
 
 (5) Includes warrants to purchase 59,018 shares of common stock.
 
 (6) Includes 1,433,864 shares of common stock which are subject to a right of
 repurchase by Arbinet, pursuant to the terms of Mr. Craig's employment
 agreement with Arbinet dated as of December 3, 1999.
 
 (7) The business address of these persons is Arbinet Holdings, Inc., 33
 Whitehall Street, 19th Floor, New York, NY 10004.
 
 (8) Excludes options to purchase 306,250 shares of common stock granted to
 Mr. Vaters under our 1997 stock incentive plan which are not exercisable
 within 60 days of March 8, 2000.
 
 (9) Includes 10,501 shares of common stock owned by Augusta Partners L.P., which
 are included as a result of Mr. Torpey's affiliation with Augusta Partners
 L.P. Excludes options to purchase 156,771 shares of common stock granted to
 Mr. Torpey under our 1997 stock incentive plan which are not exercisable
 within 60 days of March 8, 2000.
 
 (10) Excludes options to purchase 179,167 shares common stock granted to
 Mr. Hall under our 1997 stock incentive plan which are not exercisable
 within 60 days of March 8, 2000.
 
 (11) Consists of shares of common stock owned by Internet Capital Group, Inc.,
 which are included as a result of Mr. Alexander's affiliation with Internet
 Capital Group, Inc. Mr. Alexander disclaims beneficial ownership of all
 shares owned by Internet Capital Group, Inc. The business address of
 Mr. Alexander is Internet Capital Group, Inc., 800 The Safeguard Building,
 435 Devon Park Drive, Wayne, PA 19087.
 
 (12) Consists of shares of common stock owned by CB Capital Investors, L.P.
 which are included as a result of Mr. Summe's affiliation with CB Capital
 Investors, L.P. Mr. Summe disclaims beneficial ownership of all shares owned
 by CB Capital Investors, L.P. The business address of Mr. Summe is CB
 Capital Investors, L.P., 380 Madison Avenue, 12th Floor, New York, NY 10017.
 
 (13) Consists of shares of common stock owned by J.P. Morgan Investment
 Corporation and shares of common stock owned by Sixty Wall Street SBIC Fund,
 L.P., which are included as a result of Mr. Theunissen's affiliation with
 both J.P. Morgan Investment Corporation and Sixty Wall Street SBIC Fund,
 L.P. Mr. Theunissen disclaims beneficial ownership of all shares owned by
 both J.P. Morgan Investment Corporation and Sixty Wall Street SBIC Fund,
 L.P. The business address of Mr. Theunissen is J.P. Morgan Investment
 Corporation, 60 Wall Street, New York, NY 10260.
 
 (14) Consists of shares of common stock owned by Communications Ventures III,
 L.P. and shares of common stock which are owned by Communications Ventures
 III CEO & Entrepreneurs' Fund, L.P. which are included as a result of
 Mr. Van der Meer's affiliation with ComVen III, LLC, the general partner of
 each of Communications Ventures III, L.P. and Communications Ventures III
 CEO & Entrepreneurs' Fund, L.P. Mr. Van der Meer disclaims beneficial
 ownership of all shares owned by ComVen III, LLC. The business address of
 Mr. Van der Meer is ComVentures, 505 Hamilton Avenue, Suite 305, Palo Alton,
 CA 94301.
 
 (15) Includes an aggregate of 82,812 shares of common stock which are issuable
 to our directors and officers as a group under options which are exercisable
 within 60 days of March 8, 2000 and excludes an aggregate of 642,188 shares
 of common stock which are issuable to our directors and officers as a group
 under options which are not exerciseable within 60 days of March 8, 2000.
 
 The above table includes our Series A-1, C and D convertible preferred
 stock, but does not include the following transactions or arrangements with
 respect to our common stock:
 
 - 2,036,538 shares of common stock reserved for issuance upon exercise of
 options we may grant under the plan; and
 
 - the redemption of 11,980,561 shares of Series B preferred stock.
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