<PAGE>


                                                                     Exhibit 4.2

                          SERIES A WARRANT TO PURCHASE

                             SHARES OF COMMON STOCK

                                       OF

                          FIBERNET TELECOM GROUP, INC.

                            Expires December __, 2006

No.: W-A-__                                        Number of Shares: ___________
Date of Issuance: December __, 2001


         FOR VALUE RECEIVED, subject to the provisions hereinafter set forth,
the undersigned, FiberNet Telecom Group, Inc., a Delaware corporation (together
with its successors and assigns, the "Issuer"), hereby certifies that
_______________________________ or its registered assigns is entitled to
subscribe for and purchase, during the period specified in this Series A
Warrant, up to ____________________________________ (_____________) shares
(subject to adjustment as hereinafter provided) of the duly authorized, validly
issued, fully paid and non-assessable Common Stock of the Issuer, at an exercise
price per share equal to the Warrant Price then in effect, subject, however, to
the provisions and upon the terms and conditions hereinafter set forth.
Capitalized terms used in this Warrant and not otherwise defined herein shall
have the respective meanings specified in Section 8 hereof.

         1. Term. The right to subscribe for and purchase shares of Warrant
            ----
Stock represented hereby shall commence on the Shareholder Approval Date and
shall expire at 5:00 p.m., eastern time, on December __, 2006 (such period being
the "Term").

         2. Method of Exercise Payment; Issuance of New Warrant; Transfer and
            -----------------------------------------------------------------
Exchange.
--------

         (a) Time of Exercise. The purchase rights represented by this Warrant
             ----------------
may be exercised in whole or in part at any time and from time to time during
the Term commencing on the Shareholder Approval Date.

         (b) Method of Exercise. The Holder hereof may exercise this Warrant, in
             ------------------
whole or in part, by the surrender of this Warrant (with the exercise form
attached hereto duly executed) at the principal office of the Issuer, and by the
payment to the Issuer of an amount of consideration therefor equal to the
Warrant Price in effect on the date of such exercise multiplied by the number of
shares of Warrant Stock with respect to which this Warrant is then being
exercised, payable at such Holder's election (i) by certified or official bank
check or by wire transfer to an account designated by the Issuer, (ii) by
"cashless exercise" by surrender to the Issuer for cancellation of a portion of
this Warrant representing that number of unissued shares of Warrant



                                       -1-

<PAGE>


Stock which is equal to the quotient obtained by dividing (A) the product
obtained by multiplying the Warrant Price by the number of shares of Warrant
Stock being purchased upon such exercise by (B) the Per Share Market Value as of
the date of such exercise, or (iii) by a combination of the foregoing methods of
payment selected by the Holder of this Warrant. In any case where the
consideration payable upon such exercise is being paid in whole or in part
pursuant to the provisions of clause (ii) of this subsection (b), such exercise
shall be accompanied by written notice from the Holder of this Warrant
specifying the manner of payment thereof and containing a calculation showing
the number of shares of Warrant Stock with respect to which rights are being
surrendered thereunder and the net number of shares to be issued after giving
effect to such surrender.

         (c) Issuance of Stock Certificates. In the event of any exercise of the
             ------------------------------
rights represented by this Warrant in accordance with and subject to the terms
and conditions hereof, (i) certificates for the shares of Warrant Stock so
purchased shall be dated the date of such exercise and delivered to the Holder
hereof within a reasonable time, not exceeding three (3) Trading Days after such
exercise or, at the request of the Holder, issued and delivered to the
Depository Trust Company ("DTC") account on the Holder's behalf via the Deposit
Withdrawal Agent Commission System ("DWAC") within a reasonable time, not
exceeding three (3) Trading Days after such exercise, and the Holder hereof
shall be deemed for all purposes to be the Holder of the shares of Warrant Stock
so purchased as of the date of such exercise and (ii) unless this Warrant has
expired, a new Warrant representing the number of shares of Warrant Stock, if
any, with respect to which this Warrant shall not then have been exercised (less
any amount thereof which shall have been canceled in payment or partial payment
of the Warrant Price as hereinabove provided) shall also be issued to the Holder
hereof at the Issuer's expense within such time.

         (d) Transferability of Warrant. Subject to Section 2(e), this Warrant
             --------------------------
may be transferred by a Holder without the consent of the Issuer. If transferred
pursuant to this paragraph and subject to the provisions of subsection (e) of
this Section 2, this Warrant may be transferred on the books of the Issuer by
the Holder hereof in person or by duly authorized attorney, upon surrender of
this Warrant at the principal office of the Issuer, properly endorsed (by the
Holder executing an assignment in the form attached hereto) and upon payment of
any necessary transfer tax or other governmental charge imposed upon such
transfer. This Warrant is exchangeable at the principal office of the Issuer for
Warrants for the purchase of the same aggregate number of shares of Warrant
Stock, each new Warrant to represent the right to purchase such number of shares
of Warrant Stock as the Holder hereof shall designate at the time of such
exchange. All Warrants issued on transfers or exchanges shall be dated the
Original Issue Date and shall be identical with this Warrant except as to the
number of shares of Warrant Stock issuable pursuant hereto.

         (e) Continuing Rights of Holder. The Issuer will, at the time of or at
             ---------------------------
any time after each exercise of this Warrant, upon the request of the Holder
hereof, acknowledge in writing the extent, if any, of its continuing obligation
to afford to such Holder all rights to which such Holder shall continue to be
entitled after such exercise in accordance with the terms of this Warrant,
provided that if any such Holder shall fail to make any such request, the
failure shall not affect the continuing obligation of the Issuer to afford such
rights to such Holder.



                                       -2-

<PAGE>


         3. Stock Fully Paid; Reservation and Listing of Shares; Covenants.
            ---------------------------------------------------------------


         (a) Stock Fully Paid. The Issuer represents, warrants, covenants and
             ----------------
agrees that all shares of Warrant Stock which may be issued upon the exercise of
this Warrant or otherwise hereunder will, upon issuance, be duly authorized,
validly issued, fully paid and non-assessable and free from all taxes, liens and
charges created by or through Issuer. The Issuer further covenants and agrees
that during the period within which this Warrant may be exercised, the Issuer
will at all times have authorized and reserved for the purpose of the issue upon
exercise of this Warrant a sufficient number of shares of Common Stock to
provide for the exercise of this Warrant.

         (b) Reservation. If any shares of Common Stock required to be reserved
             -----------
for issuance upon exercise of this Warrant or as otherwise provided hereunder
require registration or qualification with any governmental authority under any
federal or state law before such shares may be so issued, the Issuer will in
good faith use its best efforts as expeditiously as possible at its expense to
cause such shares to be duly registered or qualified. If the Issuer shall list
any shares of Common Stock on any securities exchange or market it will, at its
expense, list thereon, maintain and increase when necessary such listing, of,
all shares of Warrant Stock from time to time issued upon exercise of this
Warrant or as otherwise provided hereunder, and, to the extent permissible under
the applicable securities exchange rules, all unissued shares of Warrant Stock
which are at any time issuable hereunder, so long as any shares of Common Stock
shall be so listed. The Issuer will also so list on each securities exchange or
market, and will maintain such listing of, any other securities which the Holder
of this Warrant shall be entitled to receive upon the exercise of this Warrant
if at the time any securities of the same class shall be listed on such
securities exchange or market by the Issuer.

         (c) Covenants. The Issuer shall not by any action including, without
             ---------
limitation, amending the Certificate of Incorporation or the by-laws of the
Issuer, or through any reorganization, transfer of assets, consolidation,
merger, dissolution, issue or sale of securities or any other action, avoid or
seek to avoid the observance or performance of any of the terms of this Warrant,
but will at all times in good faith assist in the carrying out of all such terms
and in the taking of all such actions as may be necessary or appropriate to
protect the rights of the Holder hereof against dilution (to the extent
specifically provided herein) or impairment. Without limiting the generality of
the foregoing, the Issuer will (i) not permit the par value, if any, of its
Common Stock to exceed the then effective Warrant Price, (ii) not amend or
modify any provision of the Certificate of Incorporation or by-laws of the
Issuer in any manner that would adversely affect in any way the powers,
preferences or relative participating, optional or other special rights of the
Common Stock or which would adversely affect the rights of the Holders of the
Warrants, (iii) take all such action as may be reasonably necessary in order
that the Issuer may validly and legally issue fully paid and nonassessable
shares of Common Stock, free and clear of any liens, claims, encumbrances and
restrictions (other than as provided herein) upon the exercise of this Warrant,
and (iv) use its best efforts to obtain all such authorizations, exemptions or
consents from any public regulatory body having jurisdiction thereof as may be
reasonably necessary to enable the Issuer to perform its obligations under this
Warrant.



                                       -3-

<PAGE>


         (d) Loss, Theft, Destruction of Warrants. Upon receipt of evidence
             ------------------------------------
satisfactory to the Issuer of the ownership of and the loss, theft, destruction
or mutilation of any Warrant and, in the case of any such loss, theft or
destruction, upon receipt of indemnity or security satisfactory to the Issuer
or, in the case of any such mutilation, upon surrender and cancellation of such
Warrant, the Issuer will make and deliver, in lieu of such lost, stolen,
destroyed or mutilated Warrant, a new Warrant of like tenor and representing the
right to purchase the same number of shares of Common Stock.

         4. Adjustment of Warrant Price and Warrant Share Number. The number of
            ----------------------------------------------------
shares of Common Stock for which this Warrant is exercisable, and the price at
which such shares may be purchased upon exercise of this Warrant, shall be
subject to adjustment from time to time as set forth in this Section 4. The
Issuer shall give the Holder notice of any event described below which requires
an adjustment pursuant to this Section 4 in accordance with Section 5.

         (a) Recapitalization, Reorganization, Reclassification, Consolidation,
             ------------------------------------------------------------------
Merger or Sale.
--------------

                  (i) In case the Issuer after the Original Issue Date shall do
         any of the following (each, a "Triggering Event"): (a) consolidate with
         or merge into any other Person and the Issuer shall not be the
         continuing or surviving corporation of such consolidation or merger, or
         (b) permit any other Person to consolidate with or merge into the
         Issuer and the Issuer shall be the continuing or surviving Person but,
         in connection with such consolidation or merger, any Capital Stock of
         the Issuer shall be changed into or exchanged for Securities of any
         other Person or cash or any other property, or (c) transfer all or
         substantially all of its properties or assets to any other Person, or
         (d) effect a capital reorganization or reclassification of its Capital
         Stock, then, and in the case of each such Triggering Event, proper
         provision shall be made so that, upon the basis and the terms and in
         the manner provided in this Warrant, the Holder of this Warrant shall
         be entitled (x) upon the exercise hereof at any time after the
         consummation of such Triggering Event, to the extent this Warrant is
         not exercised prior to such Triggering Event, to receive at the Warrant
         Price in effect at the time immediately prior to the consummation of
         such Triggering Event in lieu of the Common Stock issuable upon such
         exercise of this Warrant prior to such Triggering Event, the
         Securities, cash and property to which such Holder would have been
         entitled upon the consummation of such Triggering Event if such Holder
         had exercised the rights represented by this Warrant immediately prior
         thereto, subject to adjustments (subsequent to such corporate action)
         as nearly equivalent as possible to the adjustments provided for
         elsewhere in this Section 4 or (y) to sell this Warrant (or, at such
         Holder's election, a portion hereof) concurrently with the Triggering
         Event to the Person continuing after or surviving such Triggering
         Event, or to the Issuer (if Issuer is the continuing or surviving
         Person) at a sales price equal to the amount of cash, property and/or
         Securities to which a holder of the number of shares of Common Stock
         which would otherwise have been delivered upon the exercise of this
         Warrant would have been entitled upon the effective date or closing of
         any such Triggering Event (the "Event Consideration"), less the amount
         or portion of such Event Consideration having a fair value equal to the
         aggregate Warrant Price applicable to this Warrant or the portion
         hereof so sold.



                                       -4-

<PAGE>


                  (ii) Notwithstanding anything contained in this Warrant to the
         contrary, the Issuer will not effect any Triggering Event if, prior to
         the consummation thereof, each Person (other than the Issuer) which may
         be required to deliver any Securities, cash or property upon the
         exercise of this Warrant as provided herein shall assume, by written
         instrument delivered to, and reasonably satisfactory to, the Holder of
         this Warrant, (A) the obligations of the Issuer under this Warrant (and
         if the Issuer shall survive the consummation of such Triggering Event,
         such assumption shall be in addition to, and shall not release the
         Issuer from, any continuing obligations of the Issuer under this
         Warrant) and (B) the obligation to deliver to such Holder such shares
         of Securities, cash or property as, in accordance with the foregoing
         provisions of this subsection (a), such Holder shall be entitled to
         receive, and such Person shall have similarly delivered to such Holder
         an opinion of counsel for such Person, which counsel shall be
         reasonably satisfactory to such Holder, stating that this Warrant shall
         thereafter continue in full force and effect and the terms hereof
         (including, without limitation, all of the provisions of this
         subsection (a)) shall be applicable to the Securities, cash or property
         which such Person may be required to deliver upon any exercise of this
         Warrant or the exercise of any rights pursuant hereto.

                  (iii) If with respect to any Triggering Event, the Holder of
         this Warrant has exercised its right as provided in clause (y) of
         subparagraph (i) of this subsection (a) to sell this Warrant or a
         portion thereof, the Issuer agrees that as a condition to the
         consummation of any such Triggering Event the Issuer shall secure such
         right of Holder to sell this Warrant to the Person continuing after or
         surviving such Triggering Event and the Issuer shall not effect any
         such Triggering Event unless upon or prior to the consummation thereof
         the amounts of cash, property and/or Securities required under such
         clause (y) are delivered to the Holder of this Warrant. The obligation
         of the Issuer to secure such right of the Holder to sell this Warrant
         shall be subject to such Holder's cooperation with the Issuer,
         including, without limitation, the giving of customary representations
         and warranties to the purchaser in connection with any such sale. Prior
         notice of any Triggering Event shall be given to the Holder of this
         Warrant in accordance with Section 12 hereof.

         (b) Stock Dividends, Subdivisions and Combinations. If at any time the
             ----------------------------------------------
Issuer shall:

                  (i) take a record of the holders of its Common Stock for the
         purpose of entitling them to receive a dividend payable in, or other
         distribution of, Additional Shares of Common Stock,

                  (ii) subdivide its outstanding shares of Common Stock into a
         larger number of shares of Common Stock, or

                  (iii) combine its outstanding shares of Common Stock into a
         smaller number of shares of Common Stock,

then (1) the number of shares of Common Stock for which this Warrant is
exercisable immediately after the occurrence of any such event shall be adjusted
to equal the number of


                                       -5-

<PAGE>


shares of Common Stock which a record holder of the same
number of shares of Common Stock for which this Warrant is exercisable
immediately prior to the occurrence of such event would own or be entitled to
receive after the happening of such event, and (2) the Warrant Price then in
effect shall be adjusted to equal (A) the Warrant Price then in effect
multiplied by the number of shares of Common Stock for which this Warrant is
exercisable immediately prior to the adjustment divided by (B) the number of
shares of Common Stock for which this Warrant is exercisable immediately after
such adjustment.

         (c) Certain Other Distributions. If at any time the Issuer shall take a
             ---------------------------
record of the holders of its Common Stock for the purpose of entitling them to
receive any dividend or other distribution of:

                  (i) cash (other than a cash dividend payable out of earnings
         or earned surplus legally available for the payment of dividends under
         the laws of the jurisdiction of incorporation of the Issuer),

                  (ii) any evidences of its indebtedness, any shares of stock of
         any class or any other securities or property of any nature whatsoever
         (other than cash, Common Stock Equivalents or Additional Shares of
         Common Stock), or

                  (iii) any warrants or other rights to subscribe for or
         purchase any evidences of its indebtedness, any shares of stock of any
         class or any other securities or property of any nature whatsoever
         (other than cash, Common Stock Equivalents or Additional Shares of
         Common Stock),

then (1) the number of shares of Common Stock for which this Warrant is
exercisable shall be adjusted to equal the product of the number of shares of
Common Stock for which this Warrant is exercisable immediately prior to such
adjustment multiplied by a fraction (A) the numerator of which shall be the Per
Share Market Value of Common Stock at the date of taking such record and (B) the
denominator of which shall be such Per Share Market Value minus the amount
allocable to one share of Common Stock of any such cash so distributable and of
the fair value (as determined in good faith by the Board of Directors of the
Issuer and supported by an opinion from an investment banking firm of recognized
national standing acceptable to the Holder) of any and all such evidences of
indebtedness, shares of stock, other securities or property or warrants or other
subscription or purchase rights so distributable, and (2) the Warrant Price then
in effect shall be adjusted to equal (A) the Warrant Price then in effect
multiplied by the number of shares of Common Stock for which this Warrant is
exercisable immediately prior to the adjustment divided by (B) the number of
shares of Common Stock for which this Warrant is exercisable immediately after
such adjustment. A reclassification of the Common Stock (other than a change in
par value, or from par value to no par value or from no par value to par value)
into shares of Common Stock and shares of any other class of stock shall be
deemed a distribution by the Issuer to the holders of its Common Stock of such
shares of such other class of stock within the meaning of this Section 4(c) and,
if the outstanding shares of Common Stock shall be changed into a larger or
smaller number of shares of Common Stock as a part of such reclassification,
such change shall be deemed a subdivision or combination, as the case may be, of
the outstanding shares of Common Stock within the meaning of Section 4(b).



                                       -6-

<PAGE>



         (d) Issuance of Additional Shares of Common Stock.
             ---------------------------------------------

                  (i) Commencing nine months after the Original Issue Date, in
the event the Issuer, shall, at any time, from time to time, issue or sell any
Additional Shares of Common Stock (including Treasury Shares) for a
consideration per share less than the Warrant Price then in effect for the
Warrant immediately prior to the time of such issue or sale, then, forthwith
upon such issue or sale, the Warrant Price then in effect for the Warrants shall
be reduced to a price equal to the consideration per share paid for such
Additional Shares of Common Stock.

                  (ii) If at any time the Issuer shall at any time issue or sell
any Additional Shares of Common Stock in exchange for consideration in an amount
per Additional Share of Common Stock less than the Per Share Market Value at the
time the Additional Shares of Common Stock are issued or sold, then, forthwith
upon such issue or sale, the Warrant Price then in effect for the Warrants shall
be reduced by the product of the Warrant Price then in effect multiplied by the
Market Dilution Percentage and the number of shares of Common Stock for which
this Warrant is exercisable shall be increased by the product of the number of
shares of Common Stock for which this Warrant is exercisable immediately prior
to such issuance or sale multiplied by the Market Dilution Percentage. "Market
Dilution Percentage" shall mean the percentage by which such issuance or sale is
below the lesser of the Per Share Market Value or the per share market value of
the Common Stock as calculated pursuant to the terms of any other financings of
the Issuer.

                  (iii) If at any time the Issuer shall issue or sell any
Additional Shares of Common Stock in exchange for consideration in an amount per
Additional Share of Common Stock which is less than the Warrant Price or the Per
Share Market Value at the time the Additional Shares of Common Stock are issued
or sold, the adjustment required under Section 4(d) shall be made in accordance
with the formula in paragraph (i) or (ii) above which results in the lower
Warrant Price following such adjustment. The provisions of paragraphs (i) and
(ii) of Section 4(d) shall not apply to any issuance of Additional Shares of
Common Stock for which an adjustment is provided under Section 4(b) or 4(c). No
adjustment of the number of shares of Common Stock for which this Warrant shall
be exercisable shall be made under paragraph (i) or (ii) of Section 4(d) upon
the issuance of any Additional Shares of Common Stock which are issued pursuant
to the exercise of any warrants or other subscription or purchase rights or
pursuant to the exercise of any conversion or exchange rights in any Common
Stock Equivalents, if any such adjustment shall previously have been made upon
the issuance of such warrants or other rights or upon the issuance of such
Common Stock Equivalents (or upon the issuance of any warrant or other rights
therefor) pursuant to Section 4(e) or Section 4(f).

         (e) Issuance of Warrants or Other Rights. If at any time the Issuer
             ------------------------------------
shall take a record of the Holders of its Common Stock for the purpose of
entitling them to receive a distribution of, or shall in any manner (whether
directly or by assumption in a merger in which the Issuer is the surviving
corporation) issue or sell, any Common Stock Equivalents (or issue any warrant
or other rights therefor), whether or not the rights to exchange or convert
thereunder are immediately exercisable, and the price per share for which Common
Stock is issuable upon the exercise of such Common Stock Equivalents (or any
warrant or other rights therefor) shall be


                                       -7-

<PAGE>



less than the Warrant Price in effect immediately prior to the time of such
issue or sale, then the number of shares for which this Warrant is exercisable
and the Warrant Price then in effect shall be adjusted as provided in Section
4(d) on the basis that the maximum number of Additional Shares of Common Stock
issuable pursuant to all such Common Stock Equivalents (or upon the issuance of
any warrant or other rights therefor) shall be deemed to have been issued and
outstanding and the Issuer shall have received all of the consideration payable
therefor, if any, as of the date of the actual issuance of such warrants or
other rights. No adjustments of the Warrant Price then in effect or the number
of Warrant Shares for which this Warrant is exercisable shall be made upon the
actual issue of such Common Stock or of such Common Stock Equivalents upon
exercise of such warrants or other rights or upon the actual issue of such
Common Stock upon such conversion or exchange of such Common Stock Equivalents.

         (f) Issuance of Common Stock Equivalents. If at any time the Issuer
             ------------------------------------
shall take a record of the Holders of its Common Stock for the purpose of
entitling them to receive a distribution of, or shall in any manner (whether
directly or by assumption in a merger in which the Issuer is the surviving
corporation) issue or sell, any Common Stock Equivalents, whether or not the
rights to exchange or convert thereunder are immediately exercisable, and the
price per share for which Common Stock is issuable upon such conversion or
exchange shall be less than the Warrant Price in effect immediately prior to the
time of such issue or sale, then the number of shares of Common Stock for which
this Warrant is exercisable and the Warrant Price then in effect shall be
adjusted as provided in Section 4(d) on the basis that the maximum number of
Additional Shares of Common Stock necessary to effect the conversion or exchange
of all such Common Stock Equivalents shall be deemed to have been issued and
outstanding and the Issuer shall have received all of the consideration payable
therefor, if any, as of the date of actual issuance of such Common Stock
Equivalents. No further adjustment of the number of shares of Common Stock for
which this Warrant is exercisable and the Warrant Price then in effect shall be
made under this Section 4(f) upon the issuance of any Common Stock Equivalents
which are issued pursuant to the exercise of any warrants or other subscription
or purchase rights therefor, if any such adjustment shall previously have been
made upon the issuance of such warrants or other rights pursuant to Section
4(e). No further adjustments of the number of shares of Common Stock for which
this Warrant is exercisable and the Warrant Price then in effect shall be made
upon the actual issue of such Common Stock upon conversion or exchange of such
Common Stock Equivalents.

         (g) Superseding Adjustment. If, at any time after any adjustment of the
             ----------------------
number of shares of Common Stock for which this Warrant is exercisable and the
Warrant Price then in effect shall have been made pursuant to Section 4(e) or
Section 4(f) as the result of any issuance of warrants, other rights or Common
Stock Equivalents, and (i) such warrants or other rights, or the right of
conversion or exchange in such other Common Stock Equivalents, shall expire, and
all or a portion of such warrants or other rights, or the right of conversion or
exchange with respect to all or a portion of such other Common Stock
Equivalents, as the case may be shall not have been exercised, or (ii) the
consideration per share for which shares of Common Stock are issuable pursuant
to such Common Stock Equivalents, shall be increased solely by virtue of
provisions therein contained for an automatic increase in such consideration per
share upon the occurrence of a specified date or event, then for each
outstanding Warrant such previous adjustment shall be rescinded and annulled and
the Additional Shares of Common Stock which



                                       -8-

<PAGE>


were deemed to have been issued by virtue of the computation made in connection
with the adjustment so rescinded and annulled shall no longer be deemed to have
been issued by virtue of such computation. Upon the occurrence of an event set
forth in this Section 4(g) above, there shall be a recomputation made of the
effect of such Common Stock Equivalents on the basis of: (i) treating the number
of Additional Shares of Common Stock or other property, if any, theretofore
actually issued or issuable pursuant to the previous exercise of any such
warrants or other rights or any such right of conversion or exchange, as having
been issued on the date or dates of any such exercise and for the consideration
actually received and receivable therefor, and (ii) treating any such Common
Stock Equivalents which then remain outstanding as having been granted or issued
immediately after the time of such increase of the consideration per share for
which shares of Common Stock or other property are issuable under such Common
Stock Equivalents; whereupon a new adjustment of the number of shares of Common
Stock for which this Warrant is exercisable and the Warrant Price then in effect
shall be made, which new adjustment shall supersede the previous adjustment so
rescinded and annulled.

         (h) Purchase of Common Stock by the Issuer. If the Issuer at any time
             --------------------------------------
while this Warrant is outstanding shall, directly or indirectly through a
Subsidiary or otherwise, purchase, redeem or otherwise acquire any shares of
Common Stock at a price per share greater than the Per Share Market Value, then
the Warrant Price upon each such purchase, redemption or acquisition shall be
adjusted to that price determined by multiplying such Warrant Price by a
fraction (i) the numerator of which shall be the number of shares of Common
Stock outstanding immediately prior to such purchase, redemption or acquisition
minus the number of shares of Common Stock which the aggregate consideration for
the total number of such shares of Common Stock so purchased, redeemed or
acquired would purchase at the Per Share Market Value; and (ii) the denominator
of which shall be the number of shares of Common Stock outstanding immediately
after such purchase, redemption or acquisition. For the purposes of this
subsection (h), the date as of which the Per Share Market Price shall be
computed shall be the earlier of (x) the date on which the Issuer shall enter
into a firm contract for the purchase, redemption or acquisition of such Common
Stock, or (y) the date of actual purchase, redemption or acquisition of such
Common Stock. For the purposes of this subsection (h), a purchase, redemption or
acquisition of a Common Stock Equivalent shall be deemed to be a purchase of the
underlying Common Stock, and the computation herein required shall be made on
the basis of the full exercise, conversion or exchange of such Common Stock
Equivalent on the date as of which such computation is required hereby to be
made, whether or not such Common Stock Equivalent is actually exercisable,
convertible or exchangeable on such date; provided, however, that the foregoing
shall not apply to the redemption of the Issuer's series H convertible preferred
stock or Series J convertible preferred stock.

         (i) Other Provisions applicable to Adjustments under this Section. The
             -------------------------------------------------------------
following provisions shall be applicable to the making of adjustments of the
number of shares of Common Stock for which this Warrant is exercisable and the
Warrant Price then in effect provided for in this Section 4:

                  (i) Computation of Consideration. To the extent that any
                      ----------------------------
Additional Shares of Common Stock or any Common Stock Equivalents (or any
warrants or other rights therefor) shall be issued for cash consideration, the
consideration received by the Issuer therefor shall be


                                       -9-

<PAGE>


the amount of the cash received by the Issuer therefor, or, if such Additional
Shares of Common Stock or Common Stock Equivalents are offered by the Issuer for
subscription, the subscription price, or, if such Additional Shares of Common
Stock or Common Stock Equivalents are sold to underwriters or dealers for public
offering without a subscription offering, the initial public offering price (in
any such case subtracting any amounts paid or receivable for accrued interest or
accrued dividends and without taking into account any compensation, discounts or
expenses paid or incurred by the Issuer for and in the underwriting of, or
otherwise in connection with, the issuance thereof). To the extent that such
issuance shall be for a consideration other than cash, then, except as herein
otherwise expressly provided, the amount of such consideration shall be deemed
to be the fair value of such consideration at the time of such issuance as
determined in good faith by the Board of Directors of the Issuer. In case any
Additional Shares of Common Stock or any Common Stock Equivalents (or any
warrants or other rights therefor) shall be issued in connection with any merger
in which the Issuer issues any securities, the amount of consideration therefor
shall be deemed to be the fair value, as determined in good faith by the Board
of Directors of the Issuer, of such portion of the assets and business of the
nonsurviving corporation as such Board in good faith shall determine to be
attributable to such Additional Shares of Common Stock, Common Stock
Equivalents, or any warrants or other rights therefor, as the case may be. The
consideration for any Additional Shares of Common Stock issuable pursuant to any
warrants or other rights to subscribe for or purchase the same shall be the
consideration received by the Issuer for issuing such warrants or other rights
plus the additional consideration payable to the Issuer upon exercise of such
warrants or other rights. The consideration for any Additional Shares of Common
Stock issuable pursuant to the terms of any Common Stock Equivalents shall be
the consideration received by the Issuer for issuing warrants or other rights to
subscribe for or purchase such Common Stock Equivalents, plus the consideration
paid or payable to the Issuer in respect of the subscription for or purchase of
such Common Stock Equivalents, plus the additional consideration, if any,
payable to the Issuer upon the exercise of the right of conversion or exchange
in such Common Stock Equivalents. In case of the issuance at any time of any
Additional Shares of Common Stock or Common Stock Equivalents in payment or
satisfaction of any dividends upon any class of stock other than Common Stock,
the Issuer shall be deemed to have received for such Additional Shares of Common
Stock or Common Stock Equivalents a consideration equal to the amount of such
dividend so paid or satisfied.

         (ii) When Adjustments to Be Made. The adjustments required by this
              ---------------------------
Section 4 shall be made whenever and as often as any specified event requiring
an adjustment shall occur, except that any adjustment of the number of shares of
Common Stock for which this Warrant is exercisable that would otherwise be
required may be postponed (except in the case of a subdivision or combination of
shares of the Common Stock, as provided for in Section 4(b)) up to, but not
beyond the date of exercise if such adjustment either by itself or with other
adjustments not previously made adds or subtracts less than one percent (1%) of
the shares of Common Stock for which this Warrant is exercisable immediately
prior to the making of such adjustment. Any adjustment representing a change of
less than such minimum amount (except as aforesaid) which is postponed shall be
carried forward and made as soon as such adjustment, together with other
adjustments required by this Section 4 and not previously made, would result in
a minimum adjustment or on the date of exercise. For the purpose of any
adjustment, any specified event shall be deemed to have occurred at the close of
business on the date of its


                                       -10-

<PAGE>


occurrence.

         (iii) Fractional Interests. In computing adjustments under this Section
               --------------------
4, fractional interests in Common Stock shall be taken into account to the
nearest one one-hundredth (1/100th) of a share.

         (iv) When Adjustment Not Required. If the Issuer shall take a record of
              ----------------------------
the holders of its Common Stock for the purpose of entitling them to receive a
dividend or distribution or subscription or purchase rights and shall,
thereafter and before the distribution to stockholders thereof, legally abandon
its plan to pay or deliver such dividend, distribution, subscription or purchase
rights, then thereafter no adjustment shall be required by reason of the taking
of such record and any such adjustment previously made in respect thereof shall
be rescinded and annulled.

      (j) Form of Warrant after Adjustments. The form of this Warrant need not
          ---------------------------------
be changed because of any adjustments in the Warrant Price or the number and
kind of Securities purchasable upon the exercise of this Warrant.

      (k) Escrow of Warrant Stock. If after any property becomes distributable
          -----------------------
pursuant to this Section 4 by reason of the taking of any record of the holders
of Common Stock, but prior to the occurrence of the event for which such record
is taken, and the Holder exercises this Warrant, any shares of Common Stock
issuable upon exercise by reason of such adjustment shall be deemed the last
shares of Common Stock for which this Warrant is exercised (notwithstanding any
other provision to the contrary herein) and such shares or other property shall
be held in escrow for the Holder by the Issuer to be issued to the Holder upon
and to the extent that the event actually takes place, upon payment of the
current Warrant Price. Notwithstanding any other provision to the contrary
herein, if the event for which such record was taken fails to occur or is
rescinded, then such escrowed shares shall be cancelled by the Issuer and
escrowed property returned.

      5. Notice of Adjustments. Whenever the Warrant Price or Warrant Share
         ---------------------
Number shall be adjusted pursuant to Section 4 hereof (for purposes of this
Section 5, each an "adjustment"), the Issuer shall cause its Chief Financial
Officer to prepare and execute a certificate setting forth, in reasonable
detail, the event requiring the adjustment, the amount of the adjustment, the
method by which such adjustment was calculated (including a description of the
basis on which the Board made any determination hereunder), and the Warrant
Price and Warrant Share Number after giving effect to such adjustment, and shall
cause copies of such certificate to be delivered to the Holder of this Warrant
promptly after each adjustment. Any dispute between the Issuer and the Holder of
this Warrant with respect to the matters set forth in such certificate may at
the option of the Holder of this Warrant be submitted to one of the national
accounting firms currently known as the "big five" selected by the Holder,
provided that the Issuer shall have ten (10) days after receipt of notice from
such Holder of its selection of such firm to object thereto, in which case such
Holder shall select another such firm and the Issuer shall have no such right of
objection. The firm selected by the Holder of this Warrant as provided in the
preceding sentence shall be instructed to deliver a written opinion as to such
matters to the Issuer and such Holder within thirty (30) days after submission
to it of such



                                       -11-

<PAGE>


dispute. Such opinion shall be final and binding on the parties hereto. The fees
and expenses of such accounting firm shall be paid by the Issuer.


      6. Fractional Shares. No fractional shares of Warrant Stock will be issued
         -----------------
in connection with and exercise hereof, but in lieu of such fractional shares,
the Issuer shall make a cash payment therefor equal in amount to the product of
the applicable fraction multiplied by the Per Share Market Value then in effect.

      7. Ownership Cap and Certain Exercise Restrictions.
         -----------------------------------------------

      (a) Notwithstanding anything to the contrary set forth in this Warrant, at
no time may a holder of this Warrant exercise this Warrant if the number of
shares of Common Stock to be issued pursuant to such exercise would exceed, when
aggregated with all other shares of Common Stock owned by such holder at such
time, the number of shares of Common Stock which would result in such holder
owning more than 4.999% of all of the Common Stock outstanding at such time;
provided, however, that upon a holder of this Warrant providing the Issuer with
seventy-five (75) days notice (pursuant to Section 12 hereof) (the "Waiver
Notice") that such holder would like to waive this Section 7(a) with regard to
any or all shares of Common Stock issuable upon exercise of this Warrant, this
Section 7(a) will be of no force or effect with regard to all or a portion of
the Warrant referenced in the Waiver Notice.

      (b) The Holder may not exercise the Warrant hereunder to the extent such
exercise would result in the Holder beneficially owning (as determined in
accordance with Section 13(d) of the Exchange Act and the rules thereunder) in
excess of 9.999% of the then issued and outstanding shares of Common Stock,
including shares issuable upon exercise of the Warrant held by the Holder after
application of this Section; provided, however, that upon a holder of this
Warrant providing the Issuer with the 75-day Waiver Notice that such holder
would like to waive this Section 7(b) with regard to any or all shares of Common
Stock issuable upon exercise of this Warrant, this Section 7(b) will be of no
force or effect with regard to all or a portion of the Warrant referenced in the
Waiver Notice.

      8. Definitions. For the purposes of this Warrant, the following terms have
         -----------
the following meanings:

            "Additional Shares of Common Stock" means all shares of Common Stock
             ---------------------------------
      issued by the Issuer after the Original Issue Date, and all shares of
      Other Common, if any, issued by the Issuer after the Original Issue Date,
      except: (i) the Warrant Stock; (ii) issuances of up to 7,000,000 shares of
      Common Stock pursuant to the Issuer's stock option plans and employee
      stock purchase plans as they now exist or as they may be modified, amended
      or supplemented in the future; (iii) the issuance of shares of Common
      Stock in connection with the conversion of the series J convertible
      preferred stock and the Warrants and any other existing class or series of
      preferred stock or any other options, warrants or other convertible
      securities outstanding on the Original Issue Date; (iv) issuance of
      securities in connection with a strategic arrangement or alliance to
      building licensors, landlords, carriers, joint venture partners, vendors,
      consultants, lessors or lenders, and securities or instruments issued in
      connection with acquisitions so long as



                                       -12-

<PAGE>


      such issuances are not for the purpose of raising capital; (v) issuances
      in connection with strategic license agreements so long as such issuances
      are not for the purpose of raising capital; (vi) issuances to acquisition
      candidates; (vii) issuances for fees paid to an investment banker or
      advisors; (viii) issuances in public secondary offerings; (ix) issuances
      or deemed issuances of securities in connection with a repricing or
      adjustment to the exercise price of any outstanding options or warrants
      outstanding on the date of issuance of the Issuer's series J convertible
      preferred stock, provided, however, that the Company shall not reprice or
      adjust the exercise price of greater than 7,000,000 outstanding options at
      a price below $.30 (as adjusted for any stock splits, dividends,
      combinations, reclassifications, recapitalizations and similar events);
      (x) issuances of securities to the Issuer's existing lenders or
      replacement lenders; and (xi) issuances of any series J convertible
      preferred stock.

            "Board" shall mean the Board of Directors of the Issuer.
             -----

            "Capital Stock" means and includes (i) any and all shares,
             -------------
      interests, participations or other equivalents of or interests in (however
      designated) corporate stock, including, without limitation, shares of
      preferred or preference stock, (ii) all partnership interests (whether
      general or limited) in any Person which is a partnership, (iii) all
      membership interests or limited liability company interests in any limited
      liability company, and (iv) all equity or ownership interests in any
      Person of any other type.

            "Certificate of Incorporation" means the Certificate of
             ----------------------------
      Incorporation of the Issuer as in effect on the Original Issue Date, and
      as hereafter from time to time amended, modified, supplemented or restated
      in accordance with the terms hereof and thereof and pursuant to applicable
      law.

            "Common Stock" means the Common Stock, par value $.001 per share, of
             ------------
      the Issuer and any other Capital Stock into which such stock may hereafter
      be changed.

            "Common Stock Equivalent" means any Convertible Security or warrant,
             -----------------------
      option or other right to subscribe for or purchase any Additional Shares
      of Common Stock or any Convertible Security.

            "Convertible Securities" means evidences of Indebtedness, shares of
             ----------------------
      Capital Stock or other Securities which are or may be at any time
      convertible into or exchangeable for Additional Shares of Common Stock.
      The term "Convertible Security" means one of the Convertible Securities.

            "Governmental Authority" means any governmental, regulatory or
             ----------------------
      self-regulatory entity, department, body, official, authority, commission,
      board, agency or instrumentality, whether federal, state or local, and
      whether domestic or foreign.

            "Holders" mean the Persons who shall from time to time own any
             -------
      Warrant. The term "Holder" means one of the Holders.



                                       -13-

<PAGE>


            "Independent Appraiser" means a nationally recognized or major
             ---------------------
      regional investment banking firm or firm of independent certified public
      accountants of recognized standing (which may be the firm that regularly
      examines the financial statements of the Issuer) that is regularly engaged
      in the business of appraising the Capital Stock or assets of corporations
      or other entities as going concerns, and which is not affiliated with
      either the Issuer or the Holder of any Warrant.

            "Issuer" means FiberNet Telecom Group, Inc., a Delaware corporation,
             ------
      and its successors.

            "Majority Holders" means at any time the Holders of Warrants
             ----------------
      exercisable for a majority of the shares of Warrant Stock issuable under
      the Warrants at the time outstanding.

            "Nasdaq" means the Nasdaq National Market.
             ------

            "Original Issue Date" means December __, 2001.
             -------------------

            "OTC Bulletin Board" means the over-the-counter electronic bulletin
             ------------------
      board.

            "Other Common" means any other Capital Stock of the Issuer of any
             ------------
      class which shall be authorized at any time after the date of this Warrant
      (other than Common Stock) and which shall have the right to participate in
      the distribution of earnings and assets of the Issuer without limitation
      as to amount.

            "Person" means an individual, corporation, limited liability
             ------
      company, partnership, joint stock company, trust, unincorporated
      organization, joint venture, Governmental Authority or other entity of
      whatever nature.

            "Per Share Market Value" means on any particular date (a) the
             ----------------------
      closing bid price per share of the Common Stock on such date on Nasdaq or
      another registered national stock exchange on which the Common Stock is
      then listed, or if there is no such price on such date, then the closing
      bid price on such exchange or quotation system on the date nearest
      preceding such date, or (b) if the Common Stock is not listed then on
      Nasdaq or any registered national stock exchange, the closing bid price
      for a share of Common Stock in the over-the-counter market, as reported by
      the OTC Bulletin Board or in the National Quotation Bureau Incorporated or
      similar organization or agency succeeding to its functions of reporting
      prices) at the close of business on such date, or (c) if the Common Stock
      is not then reported by the OTC Bulletin Board or the National Quotation
      Bureau Incorporated (or similar organization or agency succeeding to its
      functions of reporting prices), then the average of the "Pink Sheet"
      quotes for the relevant conversion period, as determined in good faith by
      the holder, or (d) if the Common Stock is not then publicly traded the
      fair market value of a share of Common Stock as determined by an
      Independent Appraiser selected in good faith by the Majority Holders;
      provided, however, that the Issuer, after receipt of the determination by
      such Independent Appraiser, shall have the right to select an additional
      Independent Appraiser, in which


                                       -14-

<PAGE>


      case, the fair market value shall be equal to the average of the
      determinations by each such Independent Appraiser; and provided, further
      that all determinations of the Per Share Market Value shall be
      appropriately adjusted for any stock dividends, stock splits or other
      similar transactions during such period. The determination of fair market
      value by an Independent Appraiser shall be based upon the fair market
      value of the Issuer determined on a going concern basis as between a
      willing buyer and a willing seller and taking into account all relevant
      factors determinative of value, and shall be final and binding on all
      parties. In determining the fair market value of any shares of Common
      Stock, no consideration shall be given to any restrictions on transfer of
      the Common Stock imposed by agreement or by federal or state securities
      laws, or to the existence or absence of, or any limitations on, voting
      rights.

            "Purchase Agreement" means the Purchase Agreement dated as of
             ------------------
      December 6, 2001 among the Issuer and the Holder.

            "Securities" means any debt or equity securities of the Issuer,
             ----------
      whether now or hereafter authorized, any instrument convertible into or
      exchangeable for Securities or a Security, and any option, warrant or
      other right to purchase or acquire any Security. "Security" means one of
      the Securities.

            "Securities Act" means the Securities Act of 1933, as amended, or
             --------------
      any similar federal statute then in effect.

            "Shareholder Approval Date" means the date upon which the Company
             -------------------------
      obtains the vote of its shareholders as required by the applicable rules
      and regulations of the Nasdaq Stock Market, Inc. (or any successor entity)
      applicable to approve the issuance of shares of Common Stock in excess of
      19.99% of the number of shares of Common Stock outstanding immediately
      prior to the date of issuance of this Warrant.

            "Subsidiary" means any corporation at least 50% of whose outstanding
             ----------
      Voting Stock shall at the time be owned directly or indirectly by the
      Issuer or by one or more of its Subsidiaries, or by the Issuer and one or
      more of its Subsidiaries.

            "Term" has the meaning specified in Section 1 hereof.
             ----

            "Trading Day" means (a) a day on which the Common Stock is traded on
             -----------
      Nasdaq, or (b) if the Common Stock is not listed on Nasdaq, a day on which
      the Common Stock is traded on any other registered national stock
      exchange, or (c) if the Common Stock is not traded on any other registered
      national stock exchange, a day on which the Common Stock is traded on the
      OTC Bulletin Board, or (d) if the Common Stock is not traded on the OTC
      Bulletin Board, a day on which the Common Stock is quoted in the
      over-the-counter market as reported by the National Quotation Bureau
      Incorporated (or any similar organization or agency succeeding its
      functions of reporting prices); provided, however, that in the event that
      the Common Stock is not listed or quoted as set forth in (a), (b) and (c)
      hereof, then Trading Day shall mean any day except Saturday, Sunday and
      any day which shall be a legal holiday or a day on which banking
      institutions


                                       -15-

<PAGE>


      in the State of New York are authorized or required by law or other
      government action to close.

            "Voting Stock" means, as applied to the Capital Stock of any
             ------------
      corporation, Capital Stock of any class or classes (however designated)
      having ordinary voting power for the election of a majority of the members
      of the Board of Directors (or other governing body) of such corporation,
      other than Capital Stock having such power only by reason of the happening
      of a contingency.

            "Warrants" means the Warrants issued and sold pursuant to the
             --------
      Purchase Agreement, including, without limitation, this Warrant, and any
      other warrants of like tenor issued in substitution or exchange for any
      thereof pursuant to the provisions of Section 2(c), 2(d) or 2(e) hereof or
      of any of such other Warrants.

            "Warrant Price" initially means U.S. $.30, as such price may be
             -------------
      adjusted from time to time as shall result from the adjustments specified
      in this Warrant, including Section 4 hereto.

            "Warrant Share Number" means at any time the aggregate number of
             --------------------
      shares of Warrant Stock which may at such time be purchased upon exercise
      of this Warrant, after giving effect to all prior adjustments and
      increases to such number made or required to be made under the terms
      hereof.

            "Warrant Stock" means Common Stock issuable upon exercise of any
             -------------
      Warrant or Warrants or otherwise issuable pursuant to any Warrant or
      Warrants.

      9. Other Notices. In case at any time:
         -------------

            (A)   the Issuer shall make any distributions to the holders of
                  Common Stock; or

            (B)   the Issuer shall authorize the granting to all holders of its
                  Common Stock of rights to subscribe for or purchase any shares
                  of Capital Stock of any class or of any Common Stock
                  Equivalents or other rights; or

            (C)   there shall be any reclassification of the Capital Stock of
                  the Issuer; or

            (D)   there shall be any capital reorganization by the Issuer; or

            (E)   there shall be any (i) consolidation or merger involving the
                  Issuer or (ii) sale, transfer or other disposition of all or
                  substantially all of the Issuer's property, assets or business
                  (except a merger or other reorganization in which the Issuer
                  shall be the surviving corporation and its shares of Capital


                                       -16-

<PAGE>



                  Stock shall continue to be outstanding and unchanged and
                  except a consolidation, merger, sale, transfer or other
                  disposition involving a wholly-owned Subsidiary); or

            (F)   there shall be a voluntary or involuntary dissolution,
                  liquidation or winding-up of the Issuer or any partial
                  liquidation of the Issuer or distribution to holders of Common
                  Stock;

then, in each of such cases, the Issuer shall give written notice to the Holder
of the date on which (i) the books of the Issuer shall close or a record shall
be taken for such dividend, distribution or subscription rights or (ii) such
reorganization, reclassification, consolidation, merger, disposition,
dissolution, liquidation or winding-up, as the case may be, shall take place.
Such notice also shall specify the date as of which the holders of Common Stock
of record shall participate in such dividend, distribution or subscription
rights, or shall be entitled to exchange their certificates for Common Stock for
securities or other property deliverable upon such reorganization,
reclassification, consolidation, merger, disposition, dissolution, liquidation
or winding-up, as the case may be. Such notice shall be given at least twenty
(20) days prior to the action in question and not less than twenty (20) days
prior to the record date or the date on which the Issuer's transfer books are
closed in respect thereto. The Issuer shall give to the Holder notice of all
meetings and actions by written consent of its stockholders, at the same time in
the same manner as notice of any meetings of stockholders is required to be
given to stockholders who do not waive such notice (or, if such requires no
notice, then two (2) Trading Days written notice thereof describing the matters
upon which action is to be taken). The Holder shall have the right to send two
(2) representatives selected by it to each meeting, who shall be permitted to
attend, but not vote at, such meeting and any adjournments thereof. This Warrant
entitles the Holder to receive copies of all financial and other information
distributed or required to be distributed to the holders of the Common Stock.

         10. Amendment and Waiver. Any term, covenant, agreement or condition in
             --------------------
this Warrant may be amended, or compliance therewith may be waived (either
generally or in a particular instance and either retroactively or
prospectively), by a written instrument or written instruments executed by the
Issuer and the Majority Holders; provided, however, that no such amendment or
waiver shall reduce the Warrant Share Number, increase the Warrant Price,
shorten the period during which this Warrant may be exercised or modify any
provision of this Section 10 without the consent of the Holder of this Warrant.

         11. Governing Law. THIS WARRANT SHALL BE GOVERNED BY AND CONSTRUED IN
             -------------
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT GIVING EFFECT TO
PRINCIPLES OF CONFLICTS OF LAW.

         12. Notices. Any and all notices or other communications or deliveries
             -------
required or permitted to be provided hereunder shall be in writing and shall be
deemed given and effective on the earlier of (i) the date of transmission, if
such notice or communication is delivered via facsimile at the facsimile
telephone number specified for notice prior to 5:00 p.m., eastern time, on a
Trading Day, (ii) the Trading Day after the date of transmission, if such notice


                                       -17-

<PAGE>


or communication is delivered via facsimile at the facsimile telephone number
specified for notice later than 5:00 p.m., eastern time, on any date and earlier
than 11:59 p.m., eastern time, on such date, (iii) the Trading Day following the
date of mailing, if sent by nationally recognized overnight courier service or
(iv) actual receipt by the party to whom such notice is required to be given.
The addresses for such communications shall be with respect to the Holder of
this Warrant or of Warrant Stock issued pursuant hereto, addressed to such
Holder at its last known address or facsimile number appearing on the books of
the Issuer maintained for such purposes, or with respect to the Issuer,
addressed to:

                    FiberNet Telecom Group, Inc.
                    570 Lexington Avenue
                    New York, New York 10022
                    Tel. No.: (212) 405-6200
                    Fax No.:  (212) 421-8860
                    Attention: President

                    with a copy to:

                    Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
                    Chrysler Center
                    666 Third Avenue
                    New York, New York 10022
                    Tel. No.:  (212) 935-3000
                    Fax No.:  (212) 983-3115
                    Attention: Gordon Caplan

Copies of notices to the Holder shall be sent to [Jenkens & Gilchrist Parker
Chapin LLP, The Chrysler Building, 405 Lexington Avenue, New York, New York
10174, Attention: Christopher S. Auguste, Esq., Facsimile No.: (212) 704-6288]
[O'Sullivan, LLP, 30 Rockefeller Plaza, New York, New York 10112, Attention:
Audrey A. Rohan, Facsimile No.: (212) 218-6220]. Any party hereto may from time
to time change its address for notices by giving at least ten (10) days written
notice of such changed address to the other party hereto.

         13. Warrant Agent. The Issuer may, by written notice to each Holder of
             -------------
this Warrant, appoint an agent having an office in New York, New York for the
purpose of issuing shares of Warrant Stock on the exercise of this Warrant
pursuant to subsection (b) of Section 2 hereof, exchanging this Warrant pursuant
to subsection (d) of Section 2 hereof or replacing this Warrant pursuant to
subsection (d) of Section 3 hereof, or any of the foregoing, and thereafter any
such issuance, exchange or replacement, as the case may be, shall be made at
such office by such agent.

         14. Remedies. The Issuer stipulates that the remedies at law of the
             --------
Holder of this Warrant in the event of any default or threatened default by the
Issuer in the performance of or compliance with any of the terms of this Warrant
are not and will not be adequate and that, to the fullest extent permitted by
law, such terms may be specifically enforced by a decree for the



                                       -18-

<PAGE>


specific performance of any agreement contained herein or by an injunction
against a violation of any of the terms hereof or otherwise.

         15. Successors and Assigns. This Warrant and the rights evidenced
             ----------------------
hereby shall inure to the benefit of and be binding upon the successors and
assigns of the Issuer, the Holder hereof and (to the extent provided herein) the
Holders of Warrant Stock issued pursuant hereto, and shall be enforceable by any
such Holder or Holder of Warrant Stock.

         16. Modification and Severability. If, in any action before any court
             -----------------------------
or agency legally empowered to enforce any provision contained herein, any
provision hereof is found to be unenforceable, then such provision shall be
deemed modified to the extent necessary to make it enforceable by such court or
agency. If any such provision is not enforceable as set forth in the preceding
sentence, the unenforceability of such provision shall not affect the other
provisions of this Warrant, but this Warrant shall be construed as if such
unenforceable provision had never been contained herein.

         17. Headings. The headings of the Sections of this Warrant are for
             --------
convenience of reference only and shall not, for any purpose, be deemed a part
of this Warrant.



                                       -19-

<PAGE>




         IN WITNESS WHEREOF, the Issuer has executed this Warrant as of the day
and year first above written.

                          FIBERNET TELECOM GROUP, INC.

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




                                       -20-

<PAGE>



                                  EXERCISE FORM

                          FIBERNET TELECOM GROUP, INC.

The undersigned _______________, pursuant to the provisions of the within
Warrant, hereby elects to purchase _____ shares of Common Stock of FiberNet
Telecom Group, Inc. covered by the within Warrant.


Dated:                           Signature
      ----------------------               ----------------------------------

                                 Address
                                         ------------------------------------

                                         ------------------------------------


                                   ASSIGNMENT

FOR VALUE RECEIVED, _________________ hereby sells, assigns and transfers unto
__________________ the within Warrant and all rights evidenced thereby and does
irrevocably constitute and appoint _____________, attorney, to transfer the said
Warrant on the books of the within named corporation.


Dated:                           Signature
      ----------------------               ----------------------------------

                                 Address
                                         ------------------------------------

                                         ------------------------------------


                               PARTIAL ASSIGNMENT

FOR VALUE RECEIVED, _________________ hereby sells, assigns and transfers unto
__________________ the right to purchase _________ shares of Warrant Stock
evidenced by the within Warrant together with all rights therein, and does
irrevocably constitute and appoint ___________________, attorney, to transfer
that part of the said Warrant on the books of the within named corporation.


Dated:                           Signature
      ----------------------               ----------------------------------

                                 Address
                                         ------------------------------------

                                         ------------------------------------


                           FOR USE BY THE ISSUER ONLY:

This Warrant No. W-_____ canceled (or transferred or exchanged) this _____ day
of ___________, _____, shares of Common Stock issued therefor in the name of
_______________, Warrant No. W-_____ issued for ____ shares of Common Stock in
the name of _______________.

                                       -21-