<PAGE>

                                                                    EXHIBIT 4.15

                                     NOTE

$22,500,000                                                     April 11, 2000

     FOR VALUE RECEIVED, the undersigned, FIBERNET TELECOM GROUP, INC., a
Delaware corporation (the "Borrower"), unconditionally promises to pay to the
order of DEUTSCHE BANK AG NEW YORK BRANCH (the "Lender") the principal sum of
TWENTY-TWO MILLION FIVE HUNDRED THOUSAND DOLLARS ($22,500,000) or, if less, the
aggregate unpaid principal amount of all Loans (as defined in the Credit
Agreement, and as the same may be converted to Term Loans in accordance with
Section 2.1.F. of the Credit Agreement) made by the Lender pursuant to the
-------------
Credit Agreement, dated as of April 11, 2000 (as amended, supplemented, amended
and restated or otherwise modified from time to time, the "Credit Agreement"),
among the Borrower, the financial institutions (including the Lender) from time
to time parties thereto, Deutsche Bank AG New York Branch, as the administrative
agent, Deutsche Bank Securities Inc., as co-syndications agent and Toronto
Dominion (Texas), Inc., as co-syndications agent, on such dates and in such
amounts as are set forth in Section 2.5 to the Credit Agreement.  The amounts
                            -----------
payable on the Maturity Date or Term Loan Maturity Date, as applicable, may be
reduced in accordance with the terms of the Credit Agreement.  Unless otherwise
defined, terms used herein have the meanings provided in the Credit Agreement.

     The Borrower also promises to pay interest on the unpaid principal amount
hereof from time to time outstanding from and including the date hereof until
maturity (whether by acceleration or otherwise) and, after maturity, until paid,
at the rates per annum and on the dates specified in the Credit Agreement.

   Payments of both principal and interest are to be made without setoff or
counterclaim in lawful money of the United States of America in same day or
immediately available funds to the account designated by the Administrative
Agent pursuant to the Credit Agreement.

     This Note is one of the Notes referred to in, and evidences the Loans
(including, without limitation, the Term Loans) made by the Lender under, the
Credit Agreement, to which reference is made for a description of the security
for this Note and for a statement of the terms and conditions on which the
Borrower is permitted and required to make prepayments and repayments of
principal of the Indebtedness evidenced by this Note and on which such
Indebtedness may be declared to be or shall automatically become immediately due
and payable.

     Without affecting (a) the obligation of the Lender to maintain in
accordance with its usual practice an account or accounts evidencing the
Indebtedness of the Borrower to the Lender in accordance with the Credit
Agreement, (b) the Administrative Agent's obligation to maintain the Register or
(c) the provisions of Section 2.1.D(ii) of the Credit Agreement, the Lender may
                      -----------------
make (or cause to be made) appropriate notations on the grid attached to this
Note (or on any continuation of such grid).
<PAGE>

     All parties hereto, whether as makers, endorsers, or otherwise, severally
waive presentment for payment, demand, protest and notice of dishonor.  No
assignment of this Note and the obligation evidenced hereby (whether in whole or
in part) shall be effective unless it shall have been recorded in the Register
by the Administrative Agent in accordance with the terms of the Credit
Agreement.

     THIS NOTE HAS BEEN DELIVERED IN NEW YORK, NEW YORK AND SHALL BE DEEMED TO
BE A CONTRACT MADE UNDER, GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS
OF THE STATE OF NEW YORK WITHOUT REGARD TO THE CONFLICT OF LAW PROVISIONS
THEREOF, OTHER THAN SECTIONS 5-1401 AND 5-1402 OF THE GENERAL OBLIGATIONS LAW OF
THE STATE OF NEW YORK.

                                 FIBERNET TELECOM GROUP, INC.


                                 By: /s/ Jon A. Deluca
                                    ---------------------------------
                                    Name:  Jon A. Deluca
                                    Title: Vice President - Finance

                                      -2-

<PAGE>

                          LOANS AND PRINCIPAL PAYMENTS

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------------
                 Amount of
                 Loan Made                               Amount of Principal Repaid      Unpaid Principal Balance
       ---------------------------                     -----------------------------   ---------------------------
<S>      <C>          <C>             <C>                  <C>         <C>                 <C>         <C>          <C>     <C>
         Base Rate     Adjusted       Interest Period      Base Rate    Adjusted           Base Rate    Adjusted            Notation
Date                  Eurodollar      (If Applicable)                  Eurodollar                      Eurodollar   Total   Made By
                         Rate                                             Rate                            Rate
------------------------------------------------------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------------------------------------------

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

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

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

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

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

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

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

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

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

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

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

------------------------------------------------------------------------------------------------------------------------------------
</TABLE>