<PAGE>

                                                                   EXHIBIT 10.14

              AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT
              --------------------------------------------------

    THIS IS AN AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT (the
"Agreement") made and dated as of September 10, 1999 by and:
 ---------

among:  GREENWICH TECHNOLOGY PARTNERS, INC., a Delaware corporation (the
-----
        "Corporation");
         -----------

and:    the holders of shares of Series D Preferred Stock and Series E Preferred
---
        Stock of the Corporation as set forth on Exhibit A attached to this
                                                 ---------
        Agreement, including Additional Investors that purchase Series E
        Preferred Stock after the date hereof as contemplated by Section 3.11
        hereof (collectively, the "Investors"):
                                   ---------

     The Corporation and the Investors agree as follows:

     1.  DEFINITIONS.  As used in this Agreement, each of the following terms
         -----------
means:

            "Exchange Act":  The Securities Exchange Act of 1934, as amended.
             ------------

            "Form S-3": The form under the Securities Act as is in effect on the
             --------
date hereof or any successor registration form under the Securities Act
subsequently adopted by the SEC which permits inclusion or incorporation of
substantial information by reference to other documents filed by the Corporation
with the SEC.

            "Holder": Any person owning of record Registrable Securities or any
             ------
transferee of record of such Registrable Securities to whom rights under this
Agreement have been duly assigned in accordance with this Agreement.

            "Initial Public Offering": A firmly underwritten public offering
             -----------------------
pursuant to an effective registration statement under the Securities Act
covering the offer and sale of Common Stock for the account of the Corporation
in which the price per share (as adjusted for combinations, stock dividends,
subdivisions or split-ups) is at least $5.50 and the net cash proceeds to the
Corporation (after payment of underwriting discounts, commissions and fees) are
at least $30,000,000.

            "Initiating Holders": Any Holder or Holders who in the aggregate are
             ------------------
Holders of not less than 50% of the then outstanding Registrable Securities.

            "Preferred Stock": Collectively, the Series D Preferred Stock of the
             ---------------
Corporation and the Series E Preferred Stock of the Corporation.

            "Registrable Securities": All shares of Common Stock issued or
             ----------------------
issuable pursuant to the conversion of the Preferred Stock and any shares of the
Common Stock of the Corporation or other securities issued in connection with
any stock split, stock dividend, recapitalization or similar event relating to
the foregoing; excluding in all cases, however, any
<PAGE>

Registrable Securities sold by a person in a transaction in which rights under
this Agreement are not assigned in accordance with this Agreement or any
Registrable Securities sold to the public.

            "Registration": A registration effected by preparing and filing a
             ------------
registration statement in compliance with the Securities Act, and the
declaration or ordering of effectiveness of such registration statement.

            "Registration Expenses": All expenses incurred by the Corporation in
             ---------------------
complying with Sections 2.1, 2.2 and 2.3 hereof, including, without limitation,
all registration, qualification and filing fees, printing expenses, escrow fees,
fees and disbursements of counsel and accountants for the Corporation, blue sky
fees and expenses and the expense of any special audits incident to or required
by any such registration (but excluding the compensation of regular employees of
the Corporation, which shall be paid in any event by the Corporation) and the
reasonable fees and disbursements of one counsel for all Holders.

            "SEC" or "Commission": means the U.S. Securities and Exchange
             ---      ----------
Commission.

            "Securities Act":  The Securities Act of 1933, as amended.
             --------------

            "Selling Expenses":  All underwriting discounts and selling
             ----------------                               ---
commissions applicable to the sale of Registrable Securities.

     2.  REGISTRATION RIGHTS.
         -------------------

         2.1.  Requested Registration.
               ----------------------

               2.1.1. If the Corporation shall receive from an Initiating
Holder, at any time, a written request that the Corporation effect any
registration with respect to all or a part of the Registrable Securities, the
Corporation will:

                      (i)  promptly give written notice of the proposed
registration, qualification or compliance to all other Holders of Registrable
Securities; and

                      (ii) as soon as practicable, use its reasonable best
efforts to effect such registration (including, without limitation, the
execution of an undertaking to file post-effective amendments, appropriate
qualification under applicable blue sky or other state securities laws and
appropriate compliance with applicable regulations issued under the Securities
Act) as may be so requested and as would permit or facilitate the sale and
distribution of all or such portion of such Registrable Securities as are
specified in such request, together with all or such portion of the Registrable
Securities of any Holder or Holders joining in such request as are specified in
a written request received by the Corporation within 20 days after written
notice from the Corporation is given under Section 2.1.1(a)(i) above; provided,
however, that the Corporation shall not be obligated to effect, or take any
action to effect, any such registration pursuant to this Section 2.1:

                                      -2-
<PAGE>

                    (A) In any particular jurisdiction in which the Corporation
would be required to execute a general consent to service of process in
effecting such registration, qualification or compliance, unless the Corporation
is already subject to service in such jurisdiction and except as may be required
by the Securities Act or applicable rules or regulations thereunder;

                    (B) After the Corporation has effected one (1) such
registration pursuant to this Section 2.1 and such registration has been
declared or ordered effective or withdrawn by the Initiating Holders;

                    (C) If the aggregate number of all the Registrable
Securities requested by all Holders to be registered pursuant to such request
equals less than fifty percent (50%) of the total number of outstanding
Registrable Securities; or

                    (D) Prior to six months after the closing of the
Corporation's Initial Public Offering.

     The registration statement filed pursuant to the request of the Initiating
Holders may, subject to the provisions of Section 2.1.2 below, include other
securities of the Corporation which are held by officers or directors of the
Corporation for the Corporation's own account or which are held by persons who,
by virtue of agreements with the Corporation, are entitled to include their
securities in any such registration, but the Corporation and such other holders
shall have no absolute right to include any of its securities in any such
registration.

               2.1.2. If the Initiating Holders intend to distribute the
Registrable Securities covered by their request made pursuant to Section 2.1.1
hereof by means of an underwriting, they shall so advise the Corporation as a
part of their request made pursuant to Section 2.1.1 and the Corporation shall
include such information in the written notice referred to in Section 2.1.1. In
such event, the right of any Holder to include such Holder's Registrable
Securities in such registration shall be conditioned upon such Holder's
participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting (unless otherwise mutually agreed by
a majority in interest of the Initiating Holders and such Holder) to the extent
provided herein. All Holders proposing to distribute their securities through
such underwriting shall (together with the Corporation) enter into an
underwriting agreement in customary form with the underwriter or underwriters
selected for such underwriting by a majority in interest of the Initiating
Holders and reasonably acceptable to the Corporation. Notwithstanding any other
provision hereof, if the underwriter advises the Corporation and the Initiating
Holders in writing that marketing factors require a limitation of the number of
shares to be underwritten, then the Corporation shall so advise all Holders of
Registrable Securities which would otherwise be underwritten pursuant hereto and
all other holders of securities which would otherwise be underwritten pursuant
hereto, and the number of shares of Registrable Securities that may be included
in the underwriting shall be allocated first among all Holders thereof,
including the Initiating Holders, in such proportion (as nearly as practicable)
among the Holders, including the Initiating Holders, pro rata based on the
amount of Registrable Securities owned

                                      -3-
<PAGE>

by each Holder and second, if the underwriters so permit, among such additional
shares held by the holders of securities of the Corporation pro rata in
proportion to the number of shares so requested to be included in such
registration. If any Holder disapproves of the terms of such underwritten
offering, such Holder may elect to withdraw therefrom by written notice to the
Corporation, the managing underwriter and the Initiating Holders. The
Registrable Securities and or other securities held by such Holder shall be
withdrawn from registration and such Registrable Securities shall continue to be
subject to the provisions of this Agreement.

               2.1.3. Notwithstanding the foregoing, if the Corporation shall
furnish to the Holders requesting the filing of a registration statement
pursuant to this Section 2.1, a certificate signed by the President or Chief
Executive Officer of the Corporation stating either (i) that in the good faith
judgment of the Board of Directors of the Corporation, it would be seriously
detrimental to the Corporation and its shareholders for such registration
statement to be filed and it is therefore essential to defer the filing of such
registration statement, or (ii) that the Corporation intends to file its initial
registration statement within ninety (90) days following the receipt by the
Corporation of the notice by the Initiating Holders to the Corporation pursuant
to Section 2.1.1, then the Corporation shall have the right to defer such filing
for a period of not more than 90 days after receipt of the request of the
Initiating Holders; provided, however, that the Corporation may not utilize this
right more than once in any twelve (12) month period.

         2.2.  Piggyback Registrations.
               -----------------------

               2.2.1. The Corporation shall notify all Holders of Registrable
Securities in writing at least 30 days prior to filing any registration
statement under the Securities Act for purposes of effecting a public offering
of securities of the Corporation (including, but not limited to, registration
statements relating to secondary offerings of securities of the Corporation, but
excluding any registration statement relating to any employee benefit plan or a
corporate reorganization) and will afford each such Holder an opportunity to
include in such registration statement all or any part of the Registrable
Securities then held by such Holder. Each Holder desiring to include in any such
registration statement all or any part of the Registrable Securities held by
such Holder shall, within 20 days after receipt of the above-described notice
from the Corporation, so notify the Corporation in writing, and in such notice
shall inform the Corporation of the number of Registrable Securities such Holder
wishes to include in such registration statement. If a Holder decides not to
include all of its Registrable Securities in any registration statement
thereafter filed by the Corporation, such Holder shall nevertheless continue to
have the right to include any Registrable Securities in any subsequent
registration statement or registration statements as may be filed by the
Corporation with respect to offerings of its securities, all upon the terms and
conditions set forth herein.

               2.2.2. If a registration statement of which the Corporation gives
notice under Section 2.2.1 is for an underwritten offering, then the Corporation
shall so advise the Holders. In such event, the right of any such Holder to
include its Registrable Securities in a registration pursuant to this Section
2.2 shall be conditioned upon such Holder's participation in such underwriting
and the inclusion of such Holder's Registrable Securities in the underwriting to
the extent provided herein. All Holders proposing to distribute their
Registrable Securities

                                      -4-
<PAGE>

through such underwriting shall enter into an underwriting agreement in
customary form with the managing underwriter or underwriter(s) selected for such
underwriting. Notwithstanding any other provision of this Agreement, if the
managing underwriter(s) determine(s) in good faith that marketing factors
require a limitation of the number of shares to be underwritten, then the
managing underwriter(s) may exclude shares (including Registrable Securities)
from the registration and the underwriting, and the number of shares that may be
included in the registration and the underwriting shall be allocated, first, to
the Corporation, second, to each of the Holders of Registrable Securities
requesting inclusion of their Registrable Securities in such registration
statement, to be allocated among all Holders thereof pro rata based on the
amount of Registrable Securities of the Corporation owned by each Holder and
third, to each of the other holders of the Corporation's securities, other than
the Holders requesting inclusion of their Registrable Securities in such
registration statement, to be allocated among such other holders thereof pro
rata based on the number of shares of capital stock of the Corporation owned by
each such other holder; provided, however, that the right of the underwriters to
exclude shares (including Registrable Securities) from the registration and
underwriting as described above shall be restricted so that the number of
Registrable Securities included in any such registration is not reduced below
thirty percent (30%) of the total number of securities being registered in such
registration, except for a registration relating to the Corporation's Initial
Public Offering from which all Registrable Securities may be excluded. Any
Registrable Securities excluded or withdrawn from such underwriting shall be
excluded and withdrawn from the registration. For any Holder which is a
partnership or corporation, the partners, retired partners and stockholders of
such Holder, or the estates and family members of any such partners and retired
partners and any trusts for the benefit of any of the foregoing persons
collectively shall be deemed to be a single "Holder," and any pro rata reduction
with respect to such "Holder" shall be based upon the aggregate amount of shares
carrying registration rights owned by all entities and individuals included in
such "Holder," as defined in this sentence.

               2.2.3.  The Corporation shall have the right to withdraw any
registration initiated by it under this Section.

         2.3.  Form S-3 Registration.  In case the Corporation shall receive
               ---------------------
from one or more Holders a written request or requests that the Corporation
effect a registration on Form S-3 and any related qualification or compliance
with respect to all or a part of the Registrable Securities owned by such
Holders, provided the number of shares requested to be sold would have an
aggregate price to the public of at least $5,000,000, then the Corporation will:

         (i) Promptly give written notice of the proposed registration and the
Holder's request therefor, and any related qualification or compliance, to all
other Holders of Registrable Securities; and

         (ii) As soon as practicable, use its reasonable best efforts to effect
such registration on such Form S-3 and all such qualifications and compliances
as may be so requested and as would permit or facilitate the sale and
distribution of all or such portion of the Holder's Registrable Securities as
are specified in a written request received by the Corporation within 20 days
after written notice from the Corporation is given under Section 2.3(i) above;
provided,

                                      -5-
<PAGE>

however, that the Corporation shall not be obligated to effect any such
registration, qualification or compliance pursuant to this Section 2.3:

               (A) if Form S-3 is not available for such offering by the
Holders;

               (B) if the Corporation shall furnish to the Holders a certificate
signed by the President or Chief Executive Officer of the Corporation stating
that in the good faith judgment of the Board of Directors of the Corporation, it
would be seriously detrimental to the Corporation and its shareholders for such
Form S-3 Registration to be effected at such time, in which event the
Corporation shall have the right to defer the filing of the Form S-3
registration statement for an aggregate of not more than ninety (90) days after
receipt of the request of the Holders; provided however, that the Corporation
may not utilize this right more than once in any twelve (12)-month period.

               (C) in any particular jurisdiction in which the Corporation would
be required to qualify to do business or to execute a general consent to service
of process in effecting such registration, qualification or compliance; or

               (D) if the Corporation has filed a registration statement on Form
S-3 relating to Registrable Securities within the six (6) months preceding the
request of the Holders.


         2.4.  Expenses of Registration. All Registration Expenses incurred in
               ------------------------
connection with one demand registration (pursuant to Section 2.1), all piggyback
registrations (pursuant to Section 2.2) and all Form S-3 registrations (pursuant
to Section 2.3) shall be borne by the Corporation unless the expenses are in
connection with a registration subsequently withdrawn by the Holders in which
case, the Holders agree to reimburse the Corporation for such Registration
Expenses, and all Selling Expenses shall be borne by the Holders of the
securities so registered pro rata on the basis of the number of their shares so
registered.

         2.5.  Obligations of the Corporation.  Whenever required to effect the
               ------------------------------
registration of any Registrable Securities under this Agreement, the Corporation
shall, as expeditiously as reasonably possible:

               (i) Prepare and file with the SEC a registration statement with
respect to such Registrable Securities and use its reasonable best efforts to
cause such registration statement to become effective, and keep such
registration statement effective until the distribution is completed, but not
more than 180 days.

               (ii) Prepare and file with the SEC such amendments and
supplements to such registration statement and the prospectus used in connection
with such registration statement as may be necessary to comply with the
provisions of the Securities Act with respect to the disposition of all
securities covered by such registration statement.

                                      -6-
<PAGE>

               (iii)  Furnish to the Holders participating in such registration
such number of copies of a prospectus, including the registration statement and
a preliminary prospectus, if requested by any such Holder, in conformity with
the requirements of the Securities Act, and all amendments and supplements
thereto, and such other documents as they may reasonably request in order to
facilitate the disposition of the Registrable Securities owned by them that are
included in such registration.

               (iv)   Use its reasonable best efforts to register and qualify
the securities covered by such registration statement under such other
securities or Blue Sky laws of such jurisdictions as shall be reasonably
requested by the Holders, provided, however, that the Corporation shall not be
required in connection therewith or as a condition thereto to qualify to do
business or to file a general consent to service of process in any such states
or jurisdictions.

               (v)    In the event of any underwritten public offering, enter
into and perform its obligations under an underwriting agreement, in usual and
customary form, with the managing underwriter(s) of such offering. Each Holder
participating in such underwriting shall also enter into and perform its
obligations under such an agreement.

               (vi)   Notify each Holder of Registrable Securities covered by
such registration statement at any time when a prospectus relating thereto is
required to be delivered under the Securities Act of the happening of any event
of which the Corporation has knowledge as a result of which the prospectus
included in such registration statement, as then in effect, includes an untrue
statement of a material fact or omits to state a material fact required to be
stated therein or necessary to make the statements therein not misleading in the
light of the circumstances then existing and, following such notification,
promptly deliver to each Holder copies of all amendments or supplements referred
to in clauses (ii) and (iii) of this Section 2.5.

               (vii)  Use its commercially reasonable best efforts to cause all
such Registrable Securities registered pursuant to this Agreement to be listed
on each securities exchange on which similar securities issued by the
Corporation are then listed.

               (viii) Provide a transfer agent and registrar for all Registrable
Securities registered pursuant hereto and a CUSIP number for such Registrable
Securities in each case no later than the effective date of the registration.

         2.6.  Furnish Information.  It shall be a condition precedent to the
               -------------------
obligations of the Corporation to take any action pursuant to Sections 2.1, 2.2
or 2.3 that the selling Holders shall furnish to the Corporation such
information regarding themselves, the Registrable Securities held by them, and
the intended method of disposition of such securities as shall be required to
timely effect the registration of Registrable Securities.

         2.7.  Delay of Registration.  No Holder shall have any right to obtain
               ---------------------
or seek an injunction restraining or otherwise delaying any such registration as
the result of any controversy that might arise with respect to the
interpretation or implementation of this Section 2.

                                      -7-
<PAGE>

         2.8.  Indemnification.  In the event any Registrable Securities are
               ---------------
included in a registration statement  under Sections 2.1, 2.2 or 2.3:

               2.8.1. To the extent permitted by law, the Corporation will
indemnify and hold harmless each Holder, the partners, members, officers and
directors of each Holder, any underwriter (as defined in the Securities Act) for
such Holder and each person, if any, who controls such Holder or underwriter
within the meaning of the Securities Act or the Exchange Act against any losses,
claims, damages, or liabilities (joint or several) to which they may become
subject under the Securities Act, the Exchange Act or other federal or state
law, insofar as such losses, claims, damages, or liabilities (or actions in
respect thereof) arise out of or are based upon any of the following statements,
omissions or violations (collectively a "Violation"):
                                         ---------

                      (i)   any untrue statement or alleged untrue statement of
a material fact contained or incorporated by reference in such registration
statement, including any preliminary prospectus or final prospectus contained
therein or any amendments or supplements thereto;

                      (ii)  the omission or alleged omission to state therein a
material fact required to be stated therein, or necessary to make the statements
therein not misleading, or

                      (iii) any violation or alleged violation by the
Corporation of the Securities Act, the Exchange Act, any Federal or state
securities law or any rule or regulation promulgated under the Securities Act,
the Exchange Act or any Federal or state securities law in connection with the
offering covered by such registration statement;

and the Corporation will reimburse each such Holder, partner, member, officer or
director, underwriter or controlling person for any legal or other expenses
reasonably incurred by them, as incurred, in connection with investigating or
defending any such loss, claim, damage, liability or action; provided however,
that the indemnity agreement contained in this subsection 2.8.1 shall not apply
to amounts paid in settlement of any such loss, claim, damage, liability or
action if such settlement is effected without the consent of the Corporation
(which consent shall not be unreasonably withheld), nor shall the Corporation be
liable in any such case for any such loss, claim, damage, liability or action to
the extent that it arises out of or is based upon a Violation which occurs in
reliance upon and in conformity with written information furnished in writing
and expressly stated for use in connection with such registration by such
Holder, partner, member, officer, director, underwriter or controlling person of
such Holder.

               2.8.2. To the extent permitted by law, each selling Holder will,
if Registrable Securities held by such Holder are included in the registration
being effected, indemnify and hold harmless the Corporation, each of its
directors, each of its officers who have signed the registration statement, each
person, if any, who controls the Corporation within the meaning of the
Securities Act, any underwriter (as defined in the Securities Act) and any other
Holder selling securities under such registration statement or any of such other
Holder's partners, members, directors or officers or any person who controls
such underwriter or other Holder

                                      -8-
<PAGE>

within the meaning of the Securities Act or the Exchange Act, against any
losses, claims, damages or liabilities (joint or several) to which the
Corporation or any such director, officer, controlling person, underwriter or
other such Holder, member, partner or director, officer or controlling person of
such underwriter or other Holder may become subject under the Securities Act,
the Exchange Act or other federal or state law, insofar as such losses, claims,
damages or liabilities (or actions in respect thereto) arise out of or are based
upon any Violation, in each case to the extent (and only to the extent) that
such Violation occurs in reliance upon and in conformity with written
information furnished by such Holder and stated to be specifically for use in
such registration; and each such Holder will reimburse any legal or other
expenses reasonably incurred by the Corporation or any such director, officer,
controlling person, underwriter or other Holder, partner, member, officer,
director or controlling person of such other Holder or underwriter in connection
with investigating or defending any such loss, claim, damage, liability or
action; provided, however, that the indemnity agreement contained in this
subsection 2.8.2 shall not apply to amounts paid in settlement of any such loss,
claim, damage, liability or action if such settlement is effected without the
consent of the Holder, which consent shall not be unreasonably withheld; and
provided further, that the total amounts payable in indemnity by a Holder under
this Section 2.8.2 in respect of any Violation shall not exceed the net proceeds
received by such Holder in the registered offering out of which such Violation
arises.

               2.8.3. Promptly after receipt by an indemnified party under this
Section 2.8 of notice of the commencement of any action (including any
governmental action), such indemnified party will, if a claim in respect thereof
is to be made against any indemnifying party under this Section 2.8, deliver to
the indemnifying party a written notice of the commencement thereof and the
indemnifying party shall have the right to participate in, and, to the extent
the indemnifying party so desires, jointly with any other indemnifying party
similarly noticed, to assume the defense thereof with counsel mutually
satisfactory to the parties; provided, however, that an indemnified party shall
have the right to retain its own counsel, with the fees and expenses to be paid
by the indemnifying party, if representation of such indemnified party by the
counsel retained by the indemnifying party would be inappropriate due to actual
or potential conflict of interests between such indemnified party and any other
party represented by such counsel in such proceeding. The failure to deliver
written notice to the indemnifying party within a reasonable time of the
commencement of any such action, if materially prejudicial to its ability to
defend such action, shall relieve such indemnifying party of any liability to
the indemnified party under this Section 2.8, but the omission so to deliver
written notice to the indemnifying party will not relieve it of any liability
that it may have to any indemnified party otherwise than under this Section 2.8.

               2.8.4. The obligations of the Corporation and Holders under this
Section 2.8 shall survive the completion of any offering of Registrable
Securities in a registration statement, and otherwise and any transfer of
Registrable Securities by the Holder.


         2.9.  Rule 144 Reporting.  With a view to making available the
               ------------------
benefits of certain rules and regulations of the Commission which may at any
time permit the sale of the

                                      -9-
<PAGE>

Registrable Securities to the public without registration, after such time as a
public market exists for the Common Stock of the Corporation, the Corporation
agrees to:

               (a) Make and keep public information available, as those terms
are understood and defined in Rule 144 promulgated under the Securities Act, at
all times after the Corporation becomes subject to the reporting requirements of
the Exchange Act;

               (b) Use its reasonable best efforts to file with the Commission
in a timely manner all reports and other documents required of the Corporation
under the Securities Act and the Exchange Act (at any time after it has become
subject to such reporting requirements); and

               (c) So long as a Holder owns any Registrable Securities, to
furnish to the Holder forthwith upon request a written statement by the
Corporation as to its compliance with the reporting requirements of Rule 144 (at
any time after 90 days after the effective date of the first registration
statement filed by the Corporation for an offering of its securities to the
general public), and of the Securities Act and the Exchange Act (at any time
after it has become subject to the reporting requirements of the Exchange Act),
a copy of the most recent annual or quarterly report of the Corporation, and
such other reports and documents of the Corporation as a Holder may reasonably
request in availing itself of any rule or regulation of the Commission allowing
a Holder to sell any such securities without registration (at any time after the
Corporation has become subject to the reporting requirements of the Exchange
Act).

         2.10. Assignment of Registration Rights. The rights of a Holder under
               ---------------------------------
this Section 2 may be assigned by any Holder to any party in a transfer of
Registrable Securities not involving a distribution or offering of such shares
to the public and not made pursuant to Rule 144 promulgated under the Securities
Act; provided, however, in each case that such other party agrees in writing
with the Corporation to be bound by all of the provisions of this Section 2.

         2.11. Termination of Registration Rights.  The registration rights
               ----------------------------------
granted pursuant to Section 2 will terminate as to any Holder upon the later to
occur of (a) such time as Rule 144(k) is available for the resale by the then-
current Holder of all Registrable Securities then held by such Holder, (b) the
three-year anniversary following the effective date of the Corporation's Initial
Public Offering (unless such Holder is deemed an "affiliate" of the Corporation
for purposes of Rule 144) or (c) such time as a Holder has less than one percent
of the shares of the outstanding Common Stock of the Corporation (assuming
conversion of all preferred stock of the Corporation into Common Stock) and can
sell all of its remaining Registrable Securities under Rule 144 during any three
(3)-month period.

         2.12. Limitation on Subsequent Registration Rights.  From and after
               --------------------------------------------
the date hereof, the Corporation shall not enter into an agreement granting any
holder or prospective holder of any securities of the Corporation registration
rights with similar rights that are superior to the rights granted to the
Holders hereunder without the written consent of a majority of the Holders of
Registrable Securities.

                                      -10-
<PAGE>

     3.  MISCELLANEOUS.

         3.1.  Notices.  Notices given pursuant to this Agreement must be in
               -------
writing.  They shall be deemed to have been duly given:  (i) upon delivery or
refusal to accept delivery, if hand-delivered; (ii) when transmitted, if sent by
fax with confirmed receipt, followed by a "hard" copy delivered by any other
method specified in this Section 3.1; or (iii) one (1) business day after being
deposited for next-day delivery with Federal Express or other national overnight
courier service.  In each case, notices shall be addressed to the parties at
their addresses set forth on Exhibit A attached hereto or to such other place
and with such concurrent copies as the parties may subsequently designate by
written notice. The Corporation may discharge its notice obligation hereunder by
giving notice to a transferor of Registrable Securities if it has not been given
an address of the transferee.

         3.2.  Amendment; Waiver. Any term of this Agreement may be amended and
               -----------------
the observance of any term of this Agreement may be waived (either generally or
in a particular instance and either retroactively or prospectively), only with
the written consent of the party against whom enforcement of such amendment or
waiver is sought; provided, however that with respect to any Holder, the consent
of the holders of more than 50% of the Registrable Securities shall be
sufficient to bind any and all Holders; and provided, further, that where the
amendment or waiver affects a right or creates an obligation that is specific to
a party named herein (whether an individual, trust, partnership or corporation),
the amendment or waiver of such right or creation of such obligation shall
require the consent of such party.

         3.3.  Binding Effect; Assignment.  This Agreement is binding on the
               --------------------------
Corporation and the Holders and their respective heirs, personal representatives
and successors in interest.

         3.4.  Entire Agreement. The parties hereto acknowledge that this
               ----------------
written Agreement embodies the entire understanding among the parties with
respect to the registration of the Registrable Securities and amends and
restates in its entirety that certain Registration Rights Agreement dated as of
February 1, 1999, by and between the Corporation and the holders of the
Corporation's Series D Preferred Stock. There are no binding agreements or
understandings among the parties with respect to the registration of the
Registrable Securities other than as expressly set forth in this Agreement.

         3.5.  Interpretation; Construction.
               ----------------------------

               3.5.1. The terms of this Agreement have been fully negotiated by
the parties in consultation with counsel, and the wording of this Agreement has
been arrived at by all of them as a result of their joint discussions.
Accordingly, no provision of this Agreement shall be construed against a
particular party or in favor of another party merely because of which party (or
its representative) drafted or supplied the wording for such provision.

               3.5.2. Except where otherwise noted in context, all references to
"Sections"; "Exhibits" or "Schedules" shall be deemed to refer to the sections
or subsections, as appropriate, exhibits or schedules of this Agreement.

                                      -11-
<PAGE>

               3.5.3. Section headings appearing in this Agreement are inserted
solely as reference aids for the ease and convenience of the reader; they shall
not be deemed to modify, limit or define the scope or substance of the
provisions they introduce, nor shall they be used in construing the intent or
effect of such provisions.

               3.5.4. Where the context requires: (i) use of the singular or
plural incorporates the other, and (ii) pronouns and modifiers in the masculine,
feminine or neuter gender shall be deemed to refer to or include the other
genders.

               3.5.5. As used in this Agreement, the terms "include(s)" and
"including" mean "including but not limited to"; that is, in each case the
example or enumeration which follows the use of either term is illustrative but
not exclusive or exhaustive.

         3.6.  Prevailing Party. In any proceeding to enforce any provision of
               ----------------
this Agreement, the substantially prevailing party shall be entitled to recover
reasonable attorneys' fees and out-of-pocket expenses from the other party, as
determined by the court having jurisdiction.

         3.7.  Multiple Counterparts. This Agreement may be signed in one or
               ---------------------
more counterparts, all of which shall be considered one and the same agreement
and shall become effective when each of the parties has signed and delivered a
counterpart to the other.

         3.8.  Governing Law. This Agreement shall be governed by and
               -------------
interpreted according to the laws of Delaware, but without giving effect to any
Delaware choice of law provisions which might otherwise make the Laws of a
different jurisdiction govern or apply.

         3.9.  Severability.  If any provision of this Agreement is held to be
               ------------
unenforceable under applicable law, then such provision shall be excluded from
this Agreement and the balance of the Agreement shall be interpreted as if such
provision was so excluded and shall be enforceable in accordance with its terms.

         3.10. Further Assurances.  From and after the date of this Agreement,
               ------------------
upon the request of a party, the other parties shall execute and deliver such
instruments, documents or other writings as may be reasonably necessary or
desirable to confirm and carry out and to effectuate fully the intent and
purposes of this Agreement.

         3.11  Additional Investors.  As contemplated by Section 2.2 of the
               --------------------
Investment Agreement by and among the Corporation and the holders of Series E
Preferred Stock of the Corporation, by executing a counterpart signature page
hereto, each Additional Investor (as defined in the Investment Agreement) agrees
to be bound by the terms of this Agreement.

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                      -12-
<PAGE>

     IN WITNESS WHEREOF, the Corporation and the Investors have executed this
Agreement as of the day and year first above written.


                            GREENWICH TECHNOLOGY PARTNERS, INC.
                            Address:  43 Gatehouse Road
                                      Stamford, CT 06902

                            By: /s/ Dennis M. Goett
                               --------------------------------
                            Name:
                            Title:

                            VANTAGEPOINT COMMUNICATIONS PARTNERS, LP
                            Address:  One Stamford Landing, Suite 201
                                      Stamford, CT 06902

                            By: VantagePoint Communications Associates, LLC, its
                            General Partner

                            By: /s/ Jeff Marshall
                               --------------------------------
                            Name:   Jeff Marshall
                            Title: Managing Partner

                            VANTAGEPOINT VENTURE PARTNERS 1996, L.P.
                            Address:  One Stamford Landing, Suite 201
                                      Stamford, CT 06902

                            By: VantagePoint Associates, LLC
                            its General Partner

                            By:  /s/ Jeff Marshall
                               --------------------------------
                            Name:  Jeff Marshall
                            Title: Managing Partner


                            By: /s/ Dennis M. Goett
                               --------------------------------
                            Name:  Dennis M. Goett
                            Address: c/o Greenwich Technology Partners
                                     43 Gatehouse Road
                                     Stamford, CT 06902

                                     -13-
<PAGE>

                            FG-GTPD
                            Address: 20 Dayton Avenue
                                     Greenwich, CT 06830

                            By: /s/ Kathleen Shepphird
                                --------------------------------
                            Name:  Kathleen Shepphird
                            Title:  Managing Director


                            By: /s/ Carlos Dominguez
                                --------------------------------
                            Name:  Carlos Dominguez
                            Address: c/o Cisco Systems, Inc.
                                     One Penn Plaza, 5/th/ Floor
                                     New York, NY 10119


                            By: /s/ Greg Berger
                                --------------------------------
                            Name:  Greg Berger
                            Address: c/o Mack-Call Reality Group
                                     100 Clearbrook Road
                                     Elmsford, NY 10523


                            By: /s/ John Miller
                                --------------------------------
                            Name:  John Miller
                            Address: c/o Star Vest Management, Inc.
                                     712 Fifth Avenue, 34th Floor
                                     New York, NY 10019


                            By: /s/ Deborah Farrington
                                --------------------------------
                            Name:  Deborah Farrington
                            Address: c/o Star Vest Management, Inc.
                                     712 Fifth Avenue, 34th Floor
                                     New York, NY 10019

                                     -14-
<PAGE>

                            CHASE VENTURE CAPITAL ASSOCIATES, L.P.
                            Address: Attn: Jonathan R. Lynch
                                     Chase Capital Partners
                                     380 Madison Avenue, 12th Floor
                                     New York, NY 10017


                            By: /s/ Brian Richmond
                                --------------------------------
                            its General Partner

                            By:
                                --------------------------------
                            Name:
                            Title:


                            CREDIT SUISSE FIRST BOSTON VENTURE
                            FUND I, L.P.
                            Address: Attn. Steve West
                                     Credit Suisse First Boston
                                     2400 Hanover Street
                                     Palo Alto, CA 94304

                            By:  QBB MANAGEMENT FUND I, LLC,
                            its General Partner

                            By: /s/ William J. B. Brady III
                               ---------------------------------
                            Name: William J. B. Brady III
                            Title: Managing Director


                            STV PARTNERS III, L.L.C.
                            Address: 591 West Putnam Avenue
                                     Greenwich, CT 06830


                            By: /s/ Jerome C. Silvey
                                --------------------------------
                            Name:  Jerome C. Silvey
                            Title:  General Manager

                                     -15-
<PAGE>

                            FG-GTPF
                            Address: 20 Dayton Avenue
                                     Greenwich, CT 06830


                            By: /s/ Kathleen Sheppird
                                --------------------------------
                            Name:  Kathleen Sheppird
                            Title:  Managing Director

                            WHEATLEY PARTNERS II, L.P.
                            Address: c/o Geocapital Corp.
                                     767 5th Avenue
                                     New York, NY 10153


                            By: /s/ Irwin Lieber
                                --------------------------------
                            Name:  Irwin Lieber
                            Title:  General Partner

                                     -16-
<PAGE>

                              By: /s/ Edwin J. O'Mara
                                  ----------------------------------
                              Name: Edwin J. O'Mara
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/13/99
                                    --------------------------------

                              By: /s/ John Stopper
                                  ----------------------------------
                              Name: John Stopper
                                    --------------------------------
                              Title:
                                     -------------------------------
                              Date: 10/20/99
                                    --------------------------------

                              By: /s/ Laurence Pinkus
                                  ----------------------------------
                              Name: Laurence Pinkus
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/11/99
                                    --------------------------------

                              By: /s/ Kevin Bock
                                  ----------------------------------
                              Name: Kevin Bock
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/18/99
                                    --------------------------------

                              By: /s/ James Tucci
                                  ----------------------------------
                              Name: James Tucci
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/18/99
                                    --------------------------------
<PAGE>

                             By: /s/ Robert Berlin
                                --------------------------------
                              Name: Robert Berlin
                                    ----------------------------
                              Title:
                                    ----------------------------
                              Date: 10/11/99
                                    ----------------------------

                              By: /s/ John V. Wheeler
                                  ------------------------------
                              Name: John V. Wheeler
                                    ----------------------------
                              Title:
                                     ---------------------------
                              Date: 10/13/99
                                    ----------------------------

                              By: /s/ L. David Cardenas
                                  ------------------------------
                              Name: L. David Cardenas
                                    ----------------------------
                              Title:
                                    ----------------------------
                              Date: 10/11/99
                                    ----------------------------

                              By: /s/ Louis J. Mischianti
                                  ------------------------------
                              Name: Louis J. Mischianti
                                    ----------------------------
                              Title:
                                    ----------------------------
                              Date:
                                    ----------------------------

                              By: /s/ James A. Conroy
                                  ------------------------------
                              Name: James A. Conroy
                                    ----------------------------
                              Title:
                                    ----------------------------
                              Date: 10/11/99
                                    ----------------------------
<PAGE>

                              By: /s/ Emil Roymans
                                  ------------------------------
                              Name: Emil Roymans
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/15/99
                                    --------------------------------

                              By: /s/ Paul A. Rubin
                                  ----------------------------------
                              Name: Paul A. Rubin
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date:  10/11/99
                                     -------------------------------

                              By: /s/ Scott M. Freeman
                                 -----------------------------------
                              Name: Scott M. Freeman
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date:  10/12/99
                                     -------------------------------

                              By: /s/ Michael J. Schmidtberger
                                  ----------------------------------
                              Name: Michael J. Schmidtberger
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/12/99
                                    --------------------------------

                              By: /s/ Michael Grossman
                                  ----------------------------------
                              Name: Michael Grossman
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/14/99
                                    --------------------------------

                              By: /s/ Karl Frey
                                  ----------------------------------
                              Name: Karl Frey
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/11/99
                                    --------------------------------
<PAGE>

                              EPFL Partners

                              By: /s/ Russell Carpenteri
                                  ----------------------------------
                              Name: Russell Carpenteri
                                    --------------------------------
                              Title: Partner
                                     -------------------------------
                              Date:  10/12/99
                                     -------------------------------

                              By: /s/ John D. Miller
                                  ----------------------------------
                              Name: John D. Miller
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date: 10/14/99
                                    --------------------------------

                              By: /s/ Deborah A. Farrington
                                  ----------------------------------
                              Name: Deborah A. Farrington
                                    --------------------------------
                              Title:
                                    --------------------------------
                              Date:  10/14/99
                                     -------------------------------
<PAGE>

                           By: /s/ Gerard F. Becker and Christine B. Becker
                               -----------------------------------------------
                           Name: Gerard F. Becker and Christine B. Becker
                                 ---------------------------------------------
                           Title:
                                 ---------------------------------------------
                           Date: 10/13/99
                                 ---------------------------------------------

                           By: /s/ Nicholas A. Johnson and Patricia A. Johnson
                               -----------------------------------------------
                           Name: Nicholas A. Johnson and Patricia A. Johnson
                                 ---------------------------------------------
                           Title:
                                 ---------------------------------------------
                           Date: 11/29/99
                                 ---------------------------------------------

                              Clemente Family Trust


                              By: /s/ Richard Clemente
                                  ------------------------
                              Name: Richard Clemente
                                    ----------------------
                              Title: Trustee
                                     ---------------------

                              Date:  10/13/99
                                     ---------------------

                              BMZ Investments

                              By: /s/ Stacey Cox
                                  ------------------------
                              Name: Stacey E. Cox
                                    ----------------------
                              Title: Partner
                                     ---------------------
                              Date:  10/13/99
                                     ---------------------

                              By: /s/ Richard J. Testa
                                  ------------------------
                              Name: Richard J. Testa
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:
                                   -----------------------
<PAGE>

                              By: /s/ Anthony M. Carvette
                                  ------------------------
                              Name: Anthony M. Carvette
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/20/99
                                     ---------------------

                              By: /s/ Greg Berger
                                  ------------------------
                              Name: Greg Berger
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/15/99
                                     ---------------------

                              By: /s/ Kevin J. Kitson
                                  ------------------------
                              Name: Kevin J. Kitson
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/11/99
                                     ---------------------

                              By: /s/ Brian J. Flynn
                                  ------------------------
                              Name: Brian J. Flynn
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/12/99
                                     ---------------------

                              By: /s/ Angus M. Green
                                  ------------------------
                              Name: Angus M. Green
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/13/99
                                     ---------------------

                              By: /s/ Joseph A. Cabrera
                                  ------------------------
                              Name: Joseph A. Cabrera
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/14/99
                                     ---------------------
<PAGE>

                              By: /s/ Clint Heiden
                                  ------------------------
                              Name: Clint Heiden
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/16/99
                                     ---------------------

                              By: /s/ Stephen B. Seigel
                                  ------------------------
                              Name: Stephen B. Seigel
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:
                                   -----------------------

                              By: /s/ DHW Turner
                                  ------------------------
                              Name: DHW Turner
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/22/99
                                     ---------------------

                              By: /s/ Dennis M. Goett
                                  ------------------------
                              Name: Dennis M. Goett
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:
                                   -----------------------

                              IRA f/b/o Dennis M. Goett

                              By: /s/ Dennis M. Goett
                                  ------------------------
                              Name:
                                   -----------------------
                              Title:
                                    ----------------------
                              Date:  10/11/99
                                     ---------------------
<PAGE>

                           By: /s/ S. Elizabeth Press and Mark Andrew Mohn
                               -------------------------------------------
                           Name: Elizabeth Press and Mark Andrew Mohn
                                 -----------------------------------------
                           Title:
                                 -----------------------------------------
                           Date: 10/13/99
                                 -----------------------------------------

                              By: /s/ Paul C. Carey
                                  ------------------------
                              Name: Paul C. Carey
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/13/99
                                     ---------------------

                              By: /s/ Samer Tawfik
                                  ------------------------
                              Name: Samer Tawfik
                                    ----------------------
                              Title:
                                    ----------------------
                              Date:  10/14/99
                                     ---------------------

                              HIGHWOOD PARTNERS LLC

                              By: /s/ Ari Horowitz
                                  ------------------------
                              Name: Ari Horowitz
                                    ----------------------
                              Title: CEO
                                     ---------------------
                              Date:  10/14/99
                                     ---------------------

                              By: /s/ William Cox and Beatrice Cox
                                  ----------------------------------------
                              Name: William Cox and Beatrice Cox
                                    --------------------------------------
                              Title:
                                    --------------------------------------
                              Date:  10/15/99
                                     -------------------------------------
<PAGE>

                              /s/ Gregory W. Carney
                                  --------------------------
                              Name: Gregory W. Carney
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  10/15/99
                                   -------------------------



                              /s/ Paul T. Goldman
                                  --------------------------
                              Name: Paul T. Goldman
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  10/15/99
                                   -------------------------


                              /s/ Donald K. Bryan and Belinda B. Bryan
                                  ------------------------------------
                              Name: Donald K. Bryan
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  10/14/99
                                    ------------------------


                              /s/ Edward Cettina
                                  --------------------------
                              Name: Edward Cettina
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  10/17/99
                                   -------------------------


                              /s/ Elio Cettina
                                  --------------------------
                              Name: Elio Cettina
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  10/18/99
                                   -------------------------
<PAGE>

                              The CIT Group/Equity Investments, Inc.

                              /s/ Mark Vander Veen
                                  --------------------------
                              Name: Mark Vander Veen
                                   -------------------------
                              Title: Vice President
                                    ------------------------

                              Date:  10/27/99
                                   -------------------------

                              Chase Venture Capital Associates L.P.

                              /s/ Donald J. Hofmann
                                  --------------------------
                              Name: Donald J. Hofmann
                                   -------------------------
                              Title: General Partner
                                    ------------------------
                              Date:  10/19/99
                                   -------------------------


                       VantagePoint Communications Partners, L.P.
                       By: VantagePoint Communications Associate, L.L.C.,
                           Its General Partner

                       /s/ James D. Marver
                           --------------------------
                       Name: James D. Marver
                            -------------------------
                       Title:  Managing Member
                             ------------------------


                              VantagePoint Venture Partners 1996, L.P.
                              By: VantagePoint Associates, L.L.C.,
                                  Its General Partner

                              /s/ James D. Marver
                                  --------------------------
                              Name: James D. Marver
                                   -------------------------
                              Title: Managing Director
                                    ------------------------


                              /s/ Mark B. Templeton
                                  --------------------------
                              Name: Mark B. Templeton
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  12/30/99
                                   -------------------------
<PAGE>

                              /s/ Mark Wolfenberger
                                  --------------------------
                              Name: Mark Wolfenberger
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/03/00
                                   -------------------------


                              /s/ Frank P. Slattery
                                  --------------------------
                              Name: Frank P. Slattery
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  12/30/99
                                   --------------------------


                              /s/ Jeffrey A. Wrona
                                  --------------------------
                              Name: Jeffrey A. Wrona
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/04/00
                                   -------------------------


                              /s/ Michael K. Ma
                                  --------------------------
                              Name: Michael K. Ma
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/03/99
                                   -------------------------


                              /s/ Kurt Weber
                                  --------------------------
                              Name: Kurt Weber
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  12/31/99
                                   -------------------------

                              UGE Enterprises LLC

                              /s/ Roger Cozzi
                                  --------------------------
                              Name: Roger Cozzi
                                   -------------------------
                              Title: Partner
                                    ------------------------

                              Date:  01/06/00
                                   -------------------------
<PAGE>

                              Edgell Street Partners

                              /s/ James Harasimowicz
                                  --------------------------
                              Name: James Harasimowicz
                                   -------------------------
                              Title: Managing Partner
                                    ------------------------

                              Date:  01/12/00
                                   -------------------------


                              /s/ Dennis M. Goett
                                  --------------------------
                              Name: Dennis M. Goett
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  12/30/99
                                   -------------------------


                              /s/ Jill Catania
                                  --------------------------
                              Name: Jill Catania
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  12/30/99
                                   -------------------------


                              /s/ Geryl W. Darington
                                  --------------------------
                              Name: Geryl W. Darington
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  12/31/99
                                   -------------------------


                              /s/ Robert J. Garbarino
                                  --------------------------
                              Name: Robert J. Garbarino
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  12/30/99
                                   -------------------------


                              /s/ Don Henderson
                                  --------------------------
                              Name: Don Henderson
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/03/00
                                   -------------------------
<PAGE>

                              /s/ Bruce M. Tanis
                                  --------------------------
                              Name: Bruce M. Tanis
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  12/31/99
                                   -------------------------


                              /s/ Peter Cherasia
                                  --------------------------
                              Name: Peter Cherasia
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/06/00
                                   -------------------------


                              /s/ Michael A. Tunstall
                                  --------------------------
                              Name: Michael A. Tunstall
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/03/00
                                   -------------------------


                              /s/ Wayne A. Segal
                                  --------------------------
                              Name: Wayne A. Segal
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/04/00
                                   -------------------------


                              /s/ Tony Trousset
                                  --------------------------
                              Name: Tony Trousset
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/04/00
                                   -------------------------


                         /s/ S. Elizabeth Press and Mark Andrew Mohn
                             ---------------------------------------
                         Name: Elizabeth Press and Mark Andrew Mohn
                               ------------------------------------
                         Title:
                               -----------------------------
                         Date:  01/05/00
                              ------------------------------
<PAGE>

                              /s/ Richard Haverly
                                  --------------------------
                              Name: Richard Haverly
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:
                                   -------------------------

                              HIGH STREET INVESTORS 2000
                              By: Testa, Hurwitz & Thibeault, LLP

                              /s/ George W. Thibeault
                                  --------------------------
                              Name: George W. Thibeault
                                   -------------------------
                              Title: Partner
                                    ------------------------

                              Date:  01/14/00
                                   -------------------------


                              /s/ Kevin M. Barry
                                  --------------------------
                              Name: Kevin M. Barry
                                   -------------------------
                              Title:
                                    ------------------------
                              Date:  01/14/00
                                   -------------------------
<PAGE>

                             Exhibit A - Investors
                             ---------------------

<TABLE>
<CAPTION>
Holders of Series D Preferred Stock                               Registrable Securities
-----------------------------------                               ----------------------
<S>                                                               <C>
*Vantagepoint                                                           2,849,002
Communications Partners, LP
*Vantagepoint Venture                                                   1,424,502
Partners, 1996
Dennis M. Goett                                                            85,470
FG-GTPD                                                                   747,863
Carlos Dominguez                                                           42,735
Greg Berger                                                                21,368
John Miller                                                                34,188
Deborah Farrington                                                          8,547
</TABLE>

*In addition to any adjustments to the number of Registrable Securities held by
such Investor provided for in this Agreement, the number of Registrable
Securities shall be increased for such Series D Investor by the number of shares
of Common Stock issued to such Investor upon exercise of such Investor's
warrants to purchase shares of Series D Preferred Stock of the Corporation
issued on February 1, 1999 and the subsequent conversion of such shares of
Series D Preferred Stock into shares of Common Stock of the Corporation.


Holders of Series E Preferred Stock
-----------------------------------

                                Initial Closing
                                ---------------

<TABLE>
<CAPTION>
Name of Series E Investor                                                Registrable Securities
-------------------------                                                ----------------------
<S>                                                                     <C>
Chase Venture Capital Associates, L.P.                                         4,739,337
Credit Suisse First Boston Venture Fund I, L.P.                                  236,967
STV Partners III, L.L.C.                                                         473,934
FG-GTPF                                                                          236,967
Vantagepoint Communications Partners, LP                                         947,867
Vantagepoint Venture Partners 1996, L.P.                                         473,934
Wheatley Partners II L.P.                                                        473,934
</TABLE>


                           First Additional Closing
                           ------------------------

<TABLE>
<CAPTION>
Name of Series E Investor                                        Registrable Securities
-------------------------                                        ----------------------
<S>                                                              <C>
Edwin J. O'Mara                                                            7,108
John Stopper                                                              23,696
Laurence Pinkus                                                            4,739
Kevin Bock                                                                50,236
James Tucci                                                               59,241
Robert Berlin                                                             11,848
John V. Wheeler                                                           11,848
L. David Cardenas and Stacey J. Cardenas                                   2,369
Louis J. Mischianti                                                       23,696
James A. Conroy                                                            4,739
</TABLE>

                                      -i-
<PAGE>

<TABLE>
<CAPTION>
Name of Series E Investor                                        Registrable Securities
-------------------------                                        ----------------------
<S>                                                              <C>
Emil A. Roymans                                                            2,369
Paul A. Rubin                                                              7,109
Scott M. Freeman                                                           4,739
Michael J. Schmidtberger                                                   4,739
Michael A. Grossman                                                        5,924
Karl Frey                                                                 11,848
EPFL Partners                                                              4,739
John D. Miller                                                            11,848
Deborah A. Farrington                                                      2,369
Gerard F. Becker and Christine B. Becker                                  11,848
Nils A. Johnson and Patricia A. Johnson                                    9,478
Clemente Family Trust                                                      9,478
BMZ Investments                                                           23,696
Richard J. Testa                                                           9,952
Anthony M. Carvette                                                       23,696
Greg Berger                                                                5,924
Kevin J. Kitson                                                           47,393
Brian J. Flynn                                                             4,739
Angus M. Green                                                            18,957
Joseph A. Cabrera                                                         11,848
Clint Heiden                                                              23,696
Stephen B. Seigel                                                         47,393
David HW Turner                                                           11,848
Dennis M. Goett                                                           18,957
IRA FBO Dennis M. Goett                                                   28,435
S. Elizabeth Press and Mark Andrew Mohn                                   10,000
Paul C. Carey                                                             18,957
Samer Tawfik                                                             142,180
Highwood Partners LLC                                                     14,218
William C. Cox III and Beatrice I. Cox                                     9,478
Gregory W. Carney                                                         11,848
Paul T. Goldman                                                            7,109
Donald K. Bryan and Belinda B. Bryan                                      11,848
Edward Cettina                                                             7,109
Elio Cettina                                                               7,109
The CIT Group/Equity Investments, Inc.                                   473,934
Chase Venture Capital Associates, L.P.                                   473,933
VantagePoint Venture Partners 1996, L.P.                                 157,820
VantagePoint Communications Partners, L.P.                               316,114
</TABLE>

                                     -ii-
<PAGE>

                           Second Additional Closing
                           -------------------------

<TABLE>
<CAPTION>
Name of Series E Investor                                                Registrable Securities
-------------------------                                                ----------------------
<S>                                                                      <C>
Mark B. Templeton                                                                 11,848
Mark Wolfenberger                                                                 23,696
Frank P. Slattery                                                                  4,739
Jeffrey Wrona                                                                      4,739
Michael Ma                                                                         4,739
Kurt Weber                                                                        11,848
UGE Enterprises LLC                                                                4,739
Edgell Street Partners                                                             7,109
Dennis M. Goett                                                                   14,218
Jill Catania                                                                       4,739
Geryl Darington                                                                   11,848
Robert Garbarino                                                                  23,696
Donald Henderson                                                                   9,478
Bruce M. Tanis                                                                    11,848
Peter Cherasia                                                                    23,696
Michael Tunstall                                                                  35,545
Wayne A. Segal                                                                    23,696
Anthony Trousett                                                                  23,696
S. Elizabeth Press and Mark Andrew Mohn                                           20,000
Richard Haverly                                                                  100,000
High Street Investors 2000                                                        47,393
Kevin M. Barry                                                                     4,739
</TABLE>

                                     -iii-