Document:

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                                                                    Exhibit 4.33

                       [FORM OF EXCHANGE AGENT AGREEMENT]

                             _________________, 2000

The Bank of New York
101 Barclay Street
New York, NY 10286

Ladies and Gentlemen:

          Focal Communications Corporation, a Delaware corporation (the
"Company"), hereby appoints The Bank of New York, a New York banking
corporation, to act as exchange agent (the "Exchange Agent") in connection with
an exchange offer by the Company to exchange an aggregate principal amount of up
to $275,000,000 of its 11-7/8% Senior Notes due 2010, Series B (the "New
Notes"), which have been registered under the Securities Act of 1933, as
amended, for a like principal amount of its outstanding 11-7/8% Senior Notes due
2010, Series A (the "Old Notes"). The terms and conditions of the exchange offer
are set forth in a Prospectus, dated __________________, 2000 (as the same may
be amended or supplemented from time to time, the "Prospectus"), and in the
related Letter of Transmittal, which together constitute the "Exchange Offer."
Capitalized terms used herein and not defined shall have the respective meanings
ascribed thereto in the Prospectus.

          On the basis of the representations, warranties and agreements of the
Company and the Exchange Agent contained herein and subject to the terms and
conditions hereof, the following sets forth the agreement between the Company
and the Exchange Agent for the Exchange Offer:

          1.   Appointment and Duties as Exchange Agent.

          (a) The Company hereby authorizes The Bank of New York to act as
Exchange Agent in connection with the Exchange Offer and The Bank of New York
agrees to act as Exchange Agent in connection with the Exchange Offer. The
Exchange Agent will perform those services as are outlined herein, including,
but not limited to, accepting tenders of the Old Notes, assisting the Company in
the preparation of the documentation necessary to effect the transactions herein
contemplated (without assuming responsibility for such documentation, unless
such information has been furnished to the Company in writing by the Exchange
Agent).

          (b) The Company acknowledges and agrees that the Exchange Agent has
been retained pursuant to this Agreement to act solely as Exchange Agent in
connection with the Exchange Offer, and in such capacity, the Exchange Agent
shall perform such duties as are outlined herein and which are specifically set
forth in the section of the Prospectus captioned "The Exchange Offer" and in the
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Letter of Transmittal; provided, however, that in no way will the Exchange
Agent's duty to act in good faith and without gross negligence or willful
misconduct be discharged by the foregoing.

          (c) The Exchange Agent will examine each of the Letters of
Transmittal (or electronic instructions transmitted by The Depository Trust
Company (the "DTC Transmissions")) and certificates for the Old Notes and any
other documents delivered or mailed to the Exchange Agent by or for holders of
the Old Notes (or any Book-Entry Confirmations (as set forth in the Prospectus)
received by Exchange Agent with respect to the Old Notes), to ascertain whether:
(i) the Letters of Transmittal and any such other documents are duly executed
and properly completed in accordance with the instructions set forth therein (or
the DTC Transmission contains the proper information required to be set forth
therein) and (ii) the Old Notes have otherwise been properly tendered (or
the Book-Entry Confirmations are in due and proper form and contain the
information required to be set forth therein). In each case where the Letters of
Transmittal or any other documents have been improperly completed or executed
(or the DTC Transmissions are not in due and proper form or omit certain
information) or certificates for the Old Notes are not in proper form for
transfer (or the Book-Entry Confirmations are not in due and proper form or omit
certain information) or some other irregularity in connection with the tender or
acceptance of the Old Notes exists, the Exchange Agent will endeavor, subject to
the terms and conditions of the Exchange Offer, to inform the tendering holders
of Old Notes of the irregularity and to take any other action as may be
reasonably necessary or advisable to cause such irregularity to be corrected.
Notwithstanding the above, the Exchange Agent shall not be under any duty to
give any notification of any irregularities in tenders or incur any liability
for failure to give any such notification.

          (d) With the approval of the President, any Senior Vice President, any
Executive Vice President, any Vice President or the Treasurer or any Assistant
Treasurer of the Company (such approval, if given orally, to be promptly
confirmed in writing) or any other party designated by any such officer, the
Exchange Agent is authorized to waive any irregularities in connection with any
tender of the Old Notes pursuant to the Exchange Offer.

          (e) Tenders of the Old Notes may be made only as set forth in the
Letter of Transmittal and in the section of the Prospectus captioned "The
Exchange Offer" and the Old Notes shall be considered properly tendered only
when tendered in accordance with such procedures set forth therein.
Notwithstanding the provisions of this paragraph, the Old Notes which the
President, any Senior Vice President, any Executive Vice President, any Vice
President or the Treasurer, any Assistant Treasurer or any other designated
officer of the Company, shall approve (such approval, if given orally, to be
confirmed in writing) as having been properly tendered shall be considered to be
properly tendered.

          (f) The Exchange Agent shall advise the Company with respect to any
Old Notes received as soon as possible after 5:00 p.m., New York City time, on
the Expiration Date and accept its instructions with respect to disposition of
the Old Notes.

          (g) The Exchange Agent shall accept tenders:

              (i) in cases where the Old Notes are registered in two or more
          names only if signed by all named holders;

              (ii) in cases where the signing person (as indicated on the Letter
          of Transmittal) is acting in a fiduciary or a representative capacity
          only when proper evidence of his or her authority so to act is
          submitted;

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              (iii) from persons other than the registered holder of Old Notes,
          provided that customary transfer requirements, including payment of
          any applicable transfer taxes, are fulfilled; and

              (iv) in cases where the Old Notes are tendered in part only when
          such Old Notes are tendered in principal amounts of $1,000 and
          integral multiples thereof.

     The Exchange Agent shall accept partial tenders of Old Notes where so
indicated and as permitted in the Letter of Transmittal and deliver certificates
for Old Notes to the registrar for split-up and return any untendered Old Notes
to the holder (or such other person as may be designated in the Letter of
Transmittal) as promptly as practicable after expiration or termination of the
Exchange Offer.

          (h) Upon satisfaction or waiver of all of the conditions to the
Exchange Offer, the Company will notify the Exchange Agent (such notice, if
given orally, to be promptly confirmed in writing) of its acceptance, promptly
after the Expiration Date, of all Old Notes properly tendered and the Exchange
Agent, on behalf of the Company, will exchange such Old Notes for New Notes and
cause such Old Notes to be cancelled. Delivery of New Notes will be made on
behalf of the Company by the Exchange Agent at the rate of $1,000 principal
amount of New Notes for each $1,000 principal amount of the corresponding series
of Old Notes tendered promptly after notice (such notice if given orally, to be
promptly confirmed in writing) of acceptance of said Old Notes by the Company;
provided, however, that in all cases, Old Notes tendered pursuant to the
Exchange Offer will be exchanged only after timely receipt by the Exchange Agent
of certificates for such Old Notes (or confirmation of book-entry transfer into
the Exchange Agent's account at the Book-Entry Transfer Facility), a properly
completed and duly executed Letter of Transmittal (or manually signed facsimile
thereof) with any required signature guarantees and any other required
documents. The Exchange Agent shall issue New Notes only in denominations of
$1,000 or any integral multiple thereof.

          (i) Tenders pursuant to the Exchange Offer are irrevocable, except
that, subject to the terms and the conditions set forth in the Prospectus and
the Letter of Transmittal, the Old Notes tendered pursuant to the Exchange Offer
may be withdrawn at any time on or prior to the Expiration Date in accordance
with the terms of the Exchange Offer.

          (j) Notice of any decision by the Company not to exchange any Old
Notes tendered shall be given by the Company either orally (if given orally, to
be confirmed in writing) or in a written notice to the Exchange Agent.

          (k) If, pursuant to the Exchange Offer, the Company does not accept
for exchange all or part of the Old Notes tendered because of an invalid tender,
the occurrence of certain other events set forth in the Prospectus under the
caption "The Exchange Offer--Conditions to the Exchange Offer" or otherwise, the
Exchange Agent shall, upon notice from the Company (such notice if given orally,
to be confirmed in writing), promptly after the expiration or termination of the
Exchange Offer return such certificates for unaccepted Old Notes (or effect
appropriate Book-Entry Confirmation), together with any related required
documents and the Letters of Transmittal (or DTC Transmissions) relating thereto
that are in the Exchange Agent's possession, to the persons who deposited such
certificates.

          (l) Certificates for reissued Old Notes, unaccepted Old Notes or New
Notes shall be forwarded by (i) first-class certified mail, return receipt
requested, or (ii) nationally-recognized courier service.

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          (m) The Exchange Agent is not authorized to pay or offer to pay any
concessions, commissions or solicitation fees to any broker, dealer, commercial
bank, trust company or other nominee or to engage or use any person to solicit
tenders.

          (n) The Exchange Agent:

               (i) shall have no duties or obligations other than those
          specifically set forth in the Prospectus, the Letter of Transmittal or
          herein or as may be subsequently agreed to in writing;

               (ii) will make no representations and will have no
          responsibilities as to the validity, value or genuineness of any of
          the certificates for the Old Notes deposited pursuant to the Exchange
          Offer, and will not be required to and will make no representation as
          to the validity, value or genuineness of the Exchange Offer; provided,
          however, that in no way will the Exchange Agent's general duty to act
          in good faith and without gross negligence or willful misconduct be
          limited by the foregoing;

               (iii) shall not be obligated to take any legal action hereunder
          which might in the Exchange Agent's reasonable judgment involve any
          expense or liability, unless the Exchange Agent shall have been
          furnished with reasonable indemnity satisfactory to it;

               (iv) may reasonably rely on and shall be protected in acting in
          reliance upon any certificate, instrument, opinion, notice, letter,
          telegram or other document or security delivered to the Exchange Agent
          and reasonably believed by the Exchange Agent to be genuine and to
          have been signed by the proper party or parties;

               (v) may reasonably act upon any tender, statement, request,
          comment, agreement or other instrument whatsoever not only as to its
          due execution and validity and effectiveness of its provisions, but
          also as to the truth and accuracy of any information contained
          therein, which the Exchange Agent believes in good faith to be genuine
          and to have been signed or represented by a proper person or persons
          acting in a fiduciary or representative capacity (so long as proper
          evidence of such fiduciary's or representative's authority so to act
          is submitted to the Exchange Agent) and the Exchange Agent examines
          and reasonably concludes that such evidence properly establishes such
          authority;

               (vi) may conclusively rely on and shall be protected in acting
          upon written or oral instructions from the President, any Senior Vice
          President, any Executive Vice President, any Vice President, the
          Treasurer, any Assistant Treasurer or any other designated officer of
          the Company;

               (vii) may consult with counsel of its selection with respect to
          any questions relating to the Exchange Agent's duties and
          responsibilities and the opinion of such counsel shall be full and
          complete authorization and protection in respect of any

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          action taken, suffered or omitted to be taken by the Exchange Agent
          hereunder in good faith and in accordance with the opinion of such
          counsel; and

               (viii) shall not advise any person tendering Old Notes pursuant
          to the Exchange Offer as to whether to tender or refrain from
          tendering all or any portion of its Old Notes or as to the market
          value, decline or appreciation in market value of any Old Notes that
          may or may not occur as a result of the Exchange Offer or as to the
          market value of the New Notes.

          (o) The Exchange Agent shall take such action as may from time to time
be requested by the Company (and such other action as the Exchange Agent may
reasonably deem appropriate) to furnish copies of the Prospectus, Letter of
Transmittal and the Notice of Guaranteed Delivery or such other forms as may be
approved from time to time by the Company, to all persons requesting such
documents and to accept and comply with telephone requests for information
relating to the Exchange Offer, provided that such information shall relate only
to the procedures for tendering into (or withdrawing from) the Exchange Offer.
The Company will furnish you with copies of such documents at your request.

          (p) The Exchange Agent shall advise orally and promptly thereafter
confirm in writing to the Company and such other person or persons as the
Company may request, daily (and more frequently during the week immediately
preceding the Expiration Date and if otherwise reasonably requested) up to and
including the Expiration Date, the aggregate principal amount of the Old Notes
which have been duly tendered pursuant to and in compliance with the terms of
the Exchange Offer and the terms received by the Exchange Agent pursuant to the
Exchange Offer and this Agreement, separately reporting and giving cumulative
totals as to items properly received and items improperly received. In addition,
the Exchange Agent will also provide, and cooperate in making available to the
Company, or any such other person or persons upon request (such request if made
orally, to be confirmed in writing) made from time to time, such other
information as the Company may reasonably request. Such cooperation shall
include, without limitation, the granting by the Exchange Agent to the Company,
and such person or persons as the Company may request, access to those persons
on the Exchange Agent's staff who are responsible for receiving tenders, in
order to ensure that immediately prior to the Expiration Date the Company shall
have received adequate information in sufficient detail to enable the Company to
decide whether to extend the Exchange Offer. The Exchange Agent shall prepare a
final list of all persons whose tenders were accepted, the aggregate principal
amount of the Old Notes tendered, the aggregate principal amount of the Old
Notes accepted and deliver said list to the Company.

          (q) Letters of Transmittal, Book-Entry Confirmations, DTC
Transmissions and Notices of Guaranteed Delivery shall be stamped by Harris
Trust as to the date and the time of receipt thereof and shall be preserved by
the Exchange Agent for a period of time at least equal to the period of time the
Exchange Agent preserves other records pertaining to the transfer of securities.
The Exchange Agent shall dispose of unused Letters of Transmittal and other
surplus materials by returning them to the Company.

          (r) The Exchange Agent hereby expressly waives any lien, encumbrance
or right of set-off whatsoever that the Exchange Agent may have with respect to
funds deposited with it for the payment of transfer taxes by reasons of amounts,
if any, borrowed by the Company, or any of its subsidiaries

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or affiliates pursuant to any loan or credit agreement with the Exchange Agent
or for compensation owed to the Exchange Agent hereunder or for any other
matter.

          2.   Compensation.

          For services rendered as Exchange Agent hereunder, you shall be
entitled to such compensation as set forth on Schedule I attached hereto. The
provisions of this section shall survive the termination of this Agreement.

          3.   Indemnification.

          (a) The Company hereby agrees to protect, defend, fully indemnify and
hold harmless the Exchange Agent against and from any and all costs, losses,
liabilities, expenses (including reasonable counsel fees and disbursements) and
claims imposed upon or asserted against the Exchange Agent on account of any
action taken or omitted to be taken by the Exchange Agent in connection with its
acceptance of or performance of its duties under this Agreement and the
documents related thereto as well as the reasonable costs and expenses of
defending itself against any claim or liability arising out of or relating to
this Agreement and the documents related thereto. Anything in this Agreement to
the contrary notwithstanding, the Company shall not be liable for
indemnification or otherwise for any loss, liability, cost or expense to the
extent arising out of the Exchange Agent's bad faith, gross negligence or
willful misconduct. In no case shall the Company be liable under this
indemnification agreement with respect to any claim against the Exchange Agent
unless the Company shall be notified by the Exchange Agent, by letter, of the
written assertion of a claim against the Exchange Agent or of any other action
commenced against the Exchange Agent, reasonably promptly after the Exchange
Agent shall have received any such written assertion or shall have been served
with a summons in connection therewith. The Company shall be entitled to
participate at its own expense in the defense of any such claim or other action,
and, if the Company so elects, the Company may assume the defense of any pending
or threatened action against the Exchange Agent in respect of which
indemnification may be sought hereunder, in which case the Company shall not
thereafter be responsible for the fees and disbursements of legal counsel for
the Exchange Agent under this paragraph; provided that the Company shall not be
entitled to assume the defense of any such action if the named parties to such
action include both the Company and the Exchange Agent and representation of
both parties by the same legal counsel would, in the written opinion of counsel
for the Exchange Agent, be inappropriate due to actual or potential conflicting
interests between them. It is understood that the Company shall not be liable
under this paragraph for the fees and disbursements of more than one legal
counsel for the Exchange Agent. In the event that the Company shall assume the
defense of any such suit in accordance with this paragraph, the Company shall
not therewith be liable for the fees and expenses of any counsel retained by the
Exchange Agent, unless, in accordance with this paragraph, the Company is not
entitled to assume such defense, in which case the Company shall not be liable
for the fees and disbursements of more than one legal counsel for the Exchange
Agent. The provisions of this section shall survive the termination of this
Agreement.

          (b) The Exchange Agent agrees that, without the prior written consent
of the Company (which consent shall not be unreasonably withheld), it will not
settle, compromise or consent to the entry of any judgment in any pending or
threatened claim, action or proceeding in respect of which indemnification could
be sought in accordance with the indemnification provision of this Agreement
(whether or not the Exchange Agent or the Company or any of its directors,
officers and controlling persons is an actual or potential party to such claim,
action or proceeding).

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          4.   Tax Information.

          (a) The Exchange Agent shall arrange to comply with all requirements
under the tax laws of the United States, including those relating to missing Tax
Identification Numbers, and shall file any appropriate reports with the Internal
Revenue Service. The Company understands that the Exchange Agent is required, in
certain instances, to deduct 31% with respect to interest paid on the New Notes
and proceeds from the sale, exchange, redemption or retirement of the New Notes
from holders of the New Notes who have not supplied their correct Taxpayer
Identification Number or required certification. Such funds will be turned over
by the Exchange Agent to the Internal Revenue Service.

          (b) The Exchange Agent shall notify the Company of the amount of any
transfer taxes payable in respect of the exchange of the Old Notes and, upon
receipt of written approval from the Company shall deliver or cause to be
delivered, in a timely manner, to each governmental authority to which any
transfer taxes are payable in respect of the exchange of the Old Notes, the
Company's check in the amount of all transfer taxes so payable; the Exchange
Agent shall reimburse the Company for amounts refunded to the Exchange Agent in
respect of its payment of any such transfer taxes, at such time as such refund
is received by the Exchange Agent.

          5.   Governing Law.

          This Agreement shall be governed by and construed and interpreted in
accordance with the laws of the State of New York but without giving effect to
applicable principles of conflicts of law to the extent that the application of
the laws of another jurisdiction would be required thereby.

          6.   Notices.

          Any communications or notice provided for hereunder shall be in
writing and shall be given (and shall be deemed to have been given upon receipt)
by delivery in person, telecopy, or overnight delivery or by registered or
certified mail (postage prepaid, return receipt requested) to the applicable
party at the addresses indicated below:

                         If to the Exchange Agent:

                         2 North LaSalle Street, Suite 1020
                         Chicago, IL 60602
                         Telephone: (312) 827-8544
                         Telecopier No.: (312) 827-8542
                         Attention: Carolyn Potter

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                         If to the Company:

                         200 North LaSalle Street, Suite 1100
                         Chicago, IL 60601
                         Telephone: (312) 895-8400
                         Telecopier No.: (312) 895-8202
                         Attention: Renee M. Martin
                                    Senior Vice President, General
                                    Counsel and Secretary

or, as to each party, at such other address as shall be designated by such party
in a written notice complying as to delivery with the terms of this Section.

          7.   Parties in Interest.

          This Agreement shall be binding upon and inure solely to the benefit
of each party hereto and nothing in this Agreement, express or implied, is
intended to or shall confer upon any other person any right, benefit or remedy
of any nature whatsoever under or by reason of this Agreement. Without
limitation to the foregoing, the parties hereto expressly agree that no holder
of the Old Notes or the New Notes shall have any right, benefit or remedy of any
nature whatsoever under or by reason of this Agreement.

          8.   Counterparts; Severability.

          This Agreement may be executed in one or more counterparts, and by
different parties hereto on separate counterparts, each of which when so
executed shall be deemed an original, and all of such counterparts shall
together constitute one and the same agreement. If any term or other provision
of this Agreement or the application thereof is invalid, illegal or incapable of
being enforced by any rule of law, or public policy, all other provisions of
this Agreement shall nevertheless remain in full force and effect so long as the
economic or legal substance of the agreements contained herein is not affected
in any manner adverse to any party. Upon such determination that any term or
provision or the application thereof is invalid, illegal or unenforceable, the
parties hereto shall negotiate in good faith to modify this Agreement so as to
effect the original intent of the parties as closely as possible in a mutually
acceptable manner in order that the agreements contained herein may be performed
as originally contemplated to the fullest extent possible.

          9.   Headings.

          The descriptive headings contained in this Agreement are included for
convenience of reference only and shall not affect in any way the meaning or
interpretation of this Agreement.

          10.  Entire Agreement.

          This Agreement constitutes the entire understanding of the parties
hereto with respect to the subject matter hereof. This Agreement may not be
amended or modified nor may any provision hereof be waived except in writing
signed by each party to be bound thereby.

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          11.  Termination.

          This Agreement shall terminate upon the earlier of (a) the 90th day
following the expiration, withdrawal, or termination of the Exchange Offer, (b)
the close of business on the date of actual receipt of written notice by the
Exchange Agent from the Company stating that this Agreement is terminated, (c)
one year following the date of this Agreement, or (d) the time and date on which
this Agreement shall be terminated by mutual consent of the parties hereto.
Notwithstanding the foregoing, Sections 2 and 3 shall survive the termination of
this Agreement. Upon any termination of this Agreement, you shall promptly
deliver to the Company any certificates for notes, funds or property then held
by you as Exchange Agent under this Agreement.

          Kindly indicate your willingness to act as Exchange Agent and your
acceptance of the foregoing provisions by signing in the space provided below
for that purpose and returning to the Company a copy of this Agreement so
signed, whereupon this Agreement and The Bank of New York's acceptance shall
constitute a binding agreement between The Bank of New York and the Company.

                              Very truly yours,

                              FOCAL COMMUNICATIONS CORPORATION

                              By: Name: ________________________
                                  Title: _______________________

Accepted and Agreed to as of the date first written above:

THE BANK OF NEW YORK

By: Name: _______________________
    Title: ______________________

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                                  SCHEDULE I
                                  ----------

                          Exchange Agent Compensation

The Company shall:

     (i)  pay the Exchange Agent a fee for all services rendered under this
Agreement of $3,500.00; and

     (ii) reimburse the Exchange Agent for any reasonable out-of-pocket expenses
incurred as Exchange Agent in performing the services described in the
Agreement, provided, however, that the Exchange Agent shall not be entitled to
reimbursement for the fees or disbursements of its legal counsel without the
prior written consent of the Company.<PAGE>

                                                                    Exhibit 4.34

          [FORM OF 11.875% SENIOR NOTE DUE JANUARY 15, 2010, SERIES B]

CUSIP NO. 344155AE6

                                                                    $275,000,000

          Focal Communications Corporation, a Delaware corporation (herein
called the "Company", which term includes any successor Person under the
indenture referred to on the reverse of this Note) for value received, hereby
promises to pay to Cede & Co., or registered assigns, the principal amount of
two hundred seventy-five million dollars ($275,000,000) (which principal amount
may from time to time be increased or decreased to such other principal amounts
(which shall not exceed $275,000,000 at any time) by adjustments made to the
Schedule annexed hereto by the Trustee hereinafter referred to in accordance
with the indenture referred to on the reverse of this Note) on January 15, 2010.

          Interest Payment Dates:         July 15 and January 15, commencing on
                                          July 15, 2000.

          Regular Record Dates:           July 1 and January 1.

          UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE
OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE COMPANY
OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY
CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME
AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE
TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE, OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

          TRANSFERS OF THIS GLOBAL NOTE SHALL BE LIMITED TO TRANSFERS IN WHOLE,
BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH
SUCCESSOR'S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL NOTE SHALL BE
LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE
INDENTURE REFERRED TO ON THE REVERSE HEREOF.

          Reference is hereby made to the further provisions of this Note set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

          Unless the certificate of authentication hereon has been executed by
the Trustee referred to on the reverse hereof by manual signature, this Note
shall not be entitled to any benefit under the indenture referred to on the
reverse of this Note or be valid or obligatory for any purpose.
<PAGE>

          IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed.

Dated: May ___, 2000

                         FOCAL COMMUNICATIONS CORPORATION

                         By: __________________________
                             Name:
                             Title:

Attest:

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

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                               (REVERSE OF NOTE)

               11.875% SENIOR NOTE DUE JANUARY 15, 2010, SERIES B

     1.   Indenture.

          This Note is one of a duly authorized issue of Notes of the Company
designated as its 11.875% Senior Notes due January 15, 2010 (the "Notes"),
issued under an indenture, dated as of January 12, 2000 (herein, as amended from
time to time, called the "Indenture"), between the Company and Harris Trust and
Savings Bank, as trustee (herein called the "Trustee," which term includes any
successor trustee under the Indenture).  The Notes are limited in aggregate
principal amount to $275,000,000.  Reference is hereby made to the Indenture and
all indentures supplemental thereto for a statement of the respective rights,
limitations of rights, duties and immunities thereunder of the Company, the
Trustee and the Holder of this Note and of the terms upon which this Note is,
and is to be, authenticated and delivered.  All terms used in this Note which
are defined in the Indenture shall have the meanings assigned to them in the
Indenture.

     2.   Principal Amount and Interest.

          The Company will pay the principal amount of this Note on January 15,
2010.

          This Note will bear interest on the outstanding aggregate principal
amount thereof at a rate of 11.875 % per annum computed on a semiannual bond
equivalent basis from the Issue Date.

          If after a shelf registration statement registering this Note for
resale (a "Shelf Registration Statement") has been declared effective, such
Shelf Registration Statement thereafter ceases to be effective or usable
(subject to certain exceptions set forth in the Registration Agreement) in
connection with resales of this Note in accordance with and during the periods
specified in the Registration Agreement without being succeeded promptly by an
additional registration statement filed and declared effective, upon the terms
and conditions set forth in the Registration Agreement (a "Registration
Default"), then interest will accrue on this Note (in addition to the stated
interest on this Note) (the "Step-Up") and be payable in cash semiannually in
arrears on January 15 and July 15 of each year, beginning on the January 15 or
July 15 immediately following a Registration Default (such interest to be
payable to the Holder of record as of the January 1 and July 1, as the case may
be, immediately preceding such January 15 or July 15), at a rate of 0.50% per
annum during the 90-day period immediately following the occurrence of a
Registration Default and shall increase by a rate per annum equal to 0.25% at
the end of each subsequent 90-day period.  In no event shall such rate exceed
1.50% per annum in the aggregate regardless of the number of Registration
Defaults.  Interest accruing as a result of the Step Up is referred to herein as
"Additional Interest."  The amount of accrued Additional Interest shall be
determined on the basis of the number of days actually elapsed.

          The Company shall pay interest on overdue principal and premium, if
any, and interest on overdue installments of interest, to the extent lawful, at
a rate per annum equal to the interest rate payable on this Note.

          Any such interest not so punctually paid or duly provided for will
forthwith cease to be payable to the Holder on such Regular Record Date and may
either be paid to the Person in whose name this Note (or one or more Predecessor
Notes) is registered at the close of business on a Special Record Date for the
payment of such Defaulted Interest to be fixed

                                       3
<PAGE>

by the Trustee, notice of which shall be given to the Holder of this Note not
less than 10 calendar days prior to such Special Record Date.

     3.   Method of Payment.

          The Company will pay principal, premium, if any, and as provided
above, interest in money of the United States that at the time of payment is
legal tender for payment of public and private debts.  Payments in respect of
Notes represented by Global Notes (including principal, premium, interest and
Defaulted Interest, if any) will be made by wire transfer of immediately
available funds to the accounts specified by the nominee for the Depositary.
With respect to certificated Notes, the Paying Agent will make all payments of
principal, premium, interest and Defaulted Interest, if any, by wire transfer of
immediately available funds to the United States dollar accounts maintained by
the Holders entitled thereto with banks in the United States, or, if no such
account is designated by the relevant Holder to the Trustee or the Paying Agent
at least 30 days prior to the relevant due date for payment (or such other date
as the Trustee may accept in its discretion), by mailing a check to the
registered address of such Holder.  If a payment date is a date other than a
Business Day at a place of payment, payment may be made at that place on the
next succeeding day that is a Business Day and no interest shall accrue for the
intervening period.

     4.   Paying Agent and Note Registrar.

          Initially, the Trustee will act as authenticating agent, Paying Agent
and Note Registrar.  The Trustee may be removed by action of the Holders of not
less than a majority in principal amount of the outstanding Notes, or by the
Company or certain bona fide Holders of Notes upon the occurrence of certain
events.  The Company may change any Paying Agent or Note Registrar with notice
in writing to the Trustee.  The Company, any Subsidiary or any Affiliate of
either of them may act as Paying Agent or Note Registrar.

     5.   Optional Redemption.

          This Note is subject to redemption upon not less than 30 nor more than
60 days' prior written notice to each Holder of Notes to be redeemed at such
Holder's address appearing in the Note Register, in principal amounts or at any
time on or after January 15, 2005, at the following Redemption Prices plus
accrued and unpaid interest, if any, thereon to but excluding the  Redemption
Date, if redeemed during the periods indicated below:

<TABLE>
<CAPTION>
       From and Including          To and Including     Redemption Price
       ------------------          ----------------     ----------------
       <S>                         <C>                  <C>
       January 15, 2005            January 14, 2006         105.938%

       January 15, 2006            January 14, 2007         103.958%

       January 15, 2007            January 14, 2008         101.979%

       January 15, 2008 and thereafter                      100.000%
</TABLE>

          This Note will be redeemable at any time and from time to time prior
to January 15, 2003 in the event that the Company receives Net Cash Proceeds
from the sale of its Capital Stock (other than Disqualified Stock) in one or
more Public Equity Offerings, in which case the Company may, at its option, use
all or a portion of any such Net Cash Proceeds to redeem up to 35% of initially
outstanding aggregate principal amount of the Notes; provided, that at least 65%
of the original aggregate principal amount of the Notes remains outstanding
after each such redemption.  Such redemption must occur on a date of

                                       4
<PAGE>

redemption within 90 days of such sale and upon not less than 30 nor more than
60 days' prior written notice, in principal amounts of $1,000 or integral
multiples thereof at a redemption price equal to 111.875% of the principal
amount of the Notes to be redeemed plus Additional Interest, if any, to but
excluding the date of redemption.

          If, after giving effect to the offer by the Company to repurchase all
or any part of each Holder's Notes made upon the occurrence of a Change of
Control as set forth in Section 7 hereto, at least 95% of the original aggregate
principal amount of the Notes has been redeemed or repurchased pursuant to the
Indenture, the Company shall have the right to redeem the balance of the Notes
at a redemption price equal to 101% of the principal amount thereof plus accrued
and unpaid interest, if any, thereon to but excluding the date of redemption.
The Company may exercise this right by giving the Holders notice of such
redemption within 30 days following the payment date with respect to the
Company's earlier repurchase offer.

     6.   No Sinking Fund.

          The Notes do not have the benefit of any sinking fund obligations.

     7.   Repurchase of Notes at the Option of Holders upon a Change of Control.

          Upon the occurrence of a Change of Control, each Holder will have the
right to require the Company to repurchase all or any part (equal to $1,000
principal amount or an integral multiple thereof) of such Holder's Notes at a
purchase price ("Change of Control Purchase Price") equal to 101% of the
principal amount thereof plus accrued and unpaid interest, if any, thereon to
but excluding the payment date for the Change of Control Purchase Price.

          Within 30 days following any Change of Control, the Company or the
Trustee (at the expense of the Company) shall mail a notice to each Holder
regarding the Company's offer to repurchase all or any part of such Holder's
Notes.  The Holder of this Note may elect to have this Note or a portion hereof
in an authorized denomination purchased by completing the form entitled "Option
of Holder to Elect Purchase" appearing below and tendering this Note pursuant to
the offer described in the notice.  Unless the Company defaults in the payment
of the Change of Control Purchase Price with respect thereto, all Notes or
portions thereof accepted for payment pursuant to the offer described in the
notice will cease to accrue interest from and after the payment date for the
Change of Control Purchase Price.

     8.   Repurchase of Notes at the Option of Holders upon an Asset Sale.

          If at any time the Company or any Restricted Subsidiary engages in any
Asset Sale, as a result of which the aggregate amount of Excess Proceeds
calculated as of any date exceeds $5,000,000, the Company shall, within 30 days
of such date, make an offer to purchase (an "Asset Sale Offer") on a pro rata
basis (a) Notes at a purchase price (the "Offer Purchase Price") in cash equal
to 100% of the principal amount thereof, plus accrued and unpaid interest
thereon, if any, to but excluding the purchase date and (b) to the extent
required by the terms thereof, any other indebtedness of the Company that is
pari passu with the Notes.  The pro rata amount of such Excess Proceeds to be
used to purchase Notes shall be in an amount equal to the aggregate amount of
such Excess Proceeds multiplied by the quotient obtained by dividing the
principal amount of the outstanding Notes by the sum of such principal amount
and the principal amount of such other Indebtedness.  In the event the aggregate
Offer Purchase Price of the outstanding Notes tendered pursuant to an Asset Sale
Offer is in excess of the Excess Proceeds to be used to purchase such Notes,
such Excess

                                       5
<PAGE>

Proceeds shall be applied to purchase such Notes on a pro rated basis in
principal amounts of $1,000 or an integral multiple thereof.

          Within 30 days of the date the amount of Excess Proceeds exceeds
$5,000,000, the Company or the Trustee (at the expense of the Company) shall
mail to each Holder a written notice regarding the Asset Sale Offer.  The Holder
of this Note may elect to have this Note or a portion hereof in an authorized
denomination purchased by completing the form entitled "Option of Holder to
Elect Purchase" appearing below and tendering this Note pursuant to the Asset
Sale Offer.  Unless the Company defaults in the payment of the Offer Purchase
Price with respect thereto, all Notes or portions thereof selected for payment
pursuant to the Asset Sale Offer will cease to accrue interest from and after
the purchase date.

     9.   Denominations; Transfer; Exchange.

          The Notes are issuable only in registered form without coupons in
denominations of $1,000 principal amount and any integral multiple thereof.  A
Holder may register the transfer or exchange of Notes in accordance with the
Indenture.  No service charge shall be made for any such registration of
transfer or exchange, but the Company may require payment of a sum sufficient to
cover any tax or other governmental charge payable in connection therewith.

     10.  Persons Deemed Owners.

          Prior to due presentment of this Note for registration of transfer,
the Company, the Trustee, the Paying Agent and the Note Registrar may deem and
treat the Person in whose name this Note is registered as the owner hereof for
all purposes, whether or not this Note be overdue, and none of the Company, the
Trustee, the Paying Agent or the Note Registrar shall be affected by notice to
the contrary.

     11.  Unclaimed Money.

          Subject to certain notice provisions, the Trustee and the Paying Agent
shall pay to the Company upon written request any money held by them for the
payment of principal, premium, if any, or interest that remains unclaimed for
two years.  After payment to the Company, Holders entitled to such money must
look only to the Company for payment as general creditors, and all
responsibility and liability of the Trustee and the Paying Agent with respect to
such money shall cease.

     12.  Discharge Prior to Redemption.

          If the Company deposits with the Trustee United States dollars or U.S.
Government Obligations sufficient to pay the principal, premium, if any, and
accrued interest on the Notes to redemption, the Company will, with the
exceptions of certain sections thereof, be discharged from the Indenture and the
Notes, including certain covenants set forth in the Indenture.

     13.  Amendment; Waiver.

          The Indenture permits, with certain exceptions as therein provided,
the amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Holders of the Notes under the Indenture at any
time by the Company and the Trustee with the consent of the Holders of not less
than a majority in aggregate principal amount of the Notes at the time
outstanding.  The Indenture also contains provisions

                                       6
<PAGE>

permitting the Holders of not less than a majority in aggregate principal amount
of the Notes at the time outstanding, on behalf of the Holders of all the Notes,
to waive certain past defaults under the Indenture and their consequences.

     14.  Restrictive Covenants.

          The Indenture contains certain covenants which, among other things,
restrict the ability of the Company and Restricted Subsidiaries to incur
additional indebtedness (and, in the case of Restricted Subsidiaries, issue
preferred stock), pay dividends or make distributions in respect of the
Company's or Restricted Subsidiaries' capital stock, make other restricted
payments, enter into sale and leaseback transactions, incur liens, cause
encumbrances or restrictions to exist on the ability of Restricted Subsidiaries
to pay dividends or make distributions in respect of their capital stock, issue
and sell capital stock of Restricted Subsidiaries, enter into transactions with
affiliates, sell assets, or amalgamate, consolidate, merge or sell or otherwise
dispose of all or substantially all of their property and assets.

     15.  Defaults and Remedies.

          With the exception of certain Events of Defaults specified below, if
an Event of Default occurs and is continuing, the Trustee or the Holders of not
less than 25% of the aggregate principal amount of the outstanding Notes may
declare the principal amount of, and any accrued and unpaid interest on, all
Notes then outstanding to be immediately due and payable.  If a bankruptcy or
insolvency default with respect to the Company or a Restricted Subsidiary occurs
and is continuing, the Notes immediately become due and payable.  Holders may
not enforce the Indenture or the Notes except as provided in the Indenture.  The
Trustee may require indemnity satisfactory to it before it enforces the
Indenture or the Notes.  Subject to certain limitations, Holders of not less
than a majority in principal amount of the outstanding Notes will have the right
to direct the time, method and place of conducting any proceeding for exercising
any remedy available to the Trustee.

     16.  No Recourse Against Others.

          No controlling Person, director, officer, employee, incorporator or
stockholder of the Company, as such, shall have any liability for any covenant,
agreement or other obligations of the Company under the Notes or the Indenture
or for any claim based on, in respect of, or by reason of, such obligations or
their creation, solely by reason of its past, present or future status as a
controlling Person, director, officer, employee, incorporator or stockholder of
the Company.  Each Holder by accepting a Note waives and releases all such
liability (but only such liability).  The waiver and release are part of the
consideration for the issuance of the Notes.

     17.  Governing Law.

          THIS SECURITY SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
THE LAWS OF THE STATE OF NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE
PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF
ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

                                       7
<PAGE>

          The Company will furnish to any Holder upon written request and
without charge to the Holder a copy of the Indenture.  Requests may be made to:

          Focal Communications Corporation
          200 North LaSalle Street
          Chicago, Illinois 60601
          Attention: Chief Financial Officer

     18.  Ranking.

          The Notes are senior unsecured obligations of the Company ranking pari
passu in right of payment with all existing and future senior indebtedness of
the Company, and will rank senior in right of payment to all existing and future
subordinated Indebtedness of the Company.  Holders of secured Indebtedness of
the Company, however, will have claims that are prior to the claims of the
Holders with respect to the assets securing such other indebtedness except to
the extent the Notes are equally and ratably secured by such assets.

                                       8
<PAGE>

-------------------------------------------------------------------------------
                            CERTIFICATE OF TRANSFER

To assign this Note, fill in the form below:

I or we assign and transfer this Note to

     (Print or type assignee's name, address and zip code)

     (Insert assignee's soc. sec. or tax I.D. No.)

and irrevocably appoint                           agent to transfer this Note on
the books of Focal Communications Corporation.  The agent may substitute another
to act for him.

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

Date:                  Your Signature:
      ----------------                 -------------------------

-------------------------------------------------------------------------------
Sign exactly as your name appears on the other side of this Note.

                                       9
<PAGE>

In connection with any transfer of any of the Notes evidenced by this
certificate occurring prior to the expiration of the period referred to in Rule
144(k) under the Securities Act of 1933 (the "Securities Act") after the later
of the date of original issuance of such Notes and the last date, if any, on
which such Notes were owned by Focal Communications Corporation or any
Affiliate, the undersigned confirms that such Notes are being transferred in
accordance with the terms of such Notes:

CHECK ONE BOX BELOW

     (1)  [_]  to Focal Communications Corporation; or

     (2)  [_]  pursuant to an effective registration statement under the
               Securities Act; or

     (3)  [_]  inside the United States to a "qualified institutional buyer" (as
               defined in Rule 144A under the Securities Act of 1933) that
               purchases for its own account or for the account of a qualified
               institutional buyer to whom notice is given that such transfer is
               being made in reliance on Rule 144A under the Securities Act, in
               each case pursuant to and in compliance with Rule 144A under the
               Securities Act; or

     (4)  [_]  outside the United States in an offshore transaction within the
               meaning of Regulation S under the Securities Act in compliance
               with Rule 904 under the Securities Act;

     (5)  [_]  pursuant to another available exemption from registration
               provided by Rule 144 under the Securities Act; or

     (6)  [_]  to an institution that is an "accredited investor" as defined in
               Rule 501(a)(1), (2), (3) or (7) under the Securities Act that is
               acquiring this Note for investment purposes and not for
               distribution in violation of the Securities Act or any other
               applicable securities laws.

     Unless one of the boxes is checked, the Trustee will refuse to register any
     of the Notes evidenced by this certificate in the name of any person other
     than the registered holder thereof; provided, however, that if box (3),
     (4), (5) or (6) is checked, the Trustee may require, prior to registering
     any such transfer of the Notes, such legal opinions, certifications and
     other information as the Company has reasonably requested to confirm that
     such transfer is being made pursuant to an exemption from, or in a
     transaction not subject to, the registration requirements of the Securities
     Act, such as the exemption provided by Rule 144 under the Securities Act.

                                       10
<PAGE>

______________________
Signature

Signature Guarantee:

____________________________                    _______________________________
Signature must be guaranteed                    Signature
by an eligible Guarantor
Institution (banks, stock
brokers, savings and loan
associations and credit
unions) with membership in
an approved guarantee
medallion program pursuant
to Securities and Exchange
Commission Rule 17Ad-15

_______________________________________________________________________________

             TO BE COMPLETED BY PURCHASER IF (3) ABOVE IS CHECKED.

          The undersigned represents and warrants that it is purchasing this
Note for its own account or an account with respect to which it exercises sole
investment discretion and that it and any such account is a "qualified
institutional buyer" within the meaning of Rule 144A under the Securities Act,
and is aware that the sale to it is being made in reliance on Rule 144A under
the Securities Act and acknowledges that it has received such information
regarding the Company as the undersigned has requested pursuant to Rule 144A
under the Securities Act or has determined not to request such information and
that it is aware that the transferor is relying upon the foregoing
representations of the undersigned in order to claim the exemption from
registration provided by Rule 144A under the Securities Act.

Dated: ________________       _________________________________________________
                              NOTICE:  To be executed by an executive officer

                                       11
<PAGE>

               SCHEDULE OF INCREASES OR DECREASES IN GLOBAL NOTE

          The following increases or decreases in this Global Note have been
made:

<TABLE>
<CAPTION>

                 Amount of decrease in        Amount of increase in          Principal Amount of this      Signature of authorized
 Date of           Principal Amount             Principal Amount            Global Note following such     signatory of Trustee or
 Exchange         of this Global Note          of this Global Note             decrease or increase            Notes Custodian
----------      ---------------------         ---------------------         --------------------------     -----------------------
<S>             <C>                           <C>                           <C>                            <C>
</TABLE>

                                       12
<PAGE>

                       OPTION OF HOLDER TO ELECT PURCHASE

          If you want to elect to have this Note purchased by the Company
pursuant to Section 4.07 or 4.08 of the Indenture, check the box:
                                      [_]

          If you want to elect to have only part of this Note purchased by the
Company pursuant to Section 4.07 or 4.08 of the Indenture, state the amount in
principal amount ($1,000 or an integral multiple thereof): $

Date:                  Your Signature:
      ----------------                -----------------------------------------
                                      (Sign exactly as your name appears on the
                                      other side of this Note)

Signature Guarantee:
                     ----------------------------------------------------------
                     Signature must be guaranteed by an eligible Guarantor
                     Institution (banks, stock brokers, savings and loan
                     associations and credit unions) with membership in an
                     approved guarantee medallion program pursuant to Securities
                     and Exchange Commission Rule 17Ad-15.

                                       13
<PAGE>

          The Bank of New York, as successor Trustee to Harris Trust and Savings
Bank under Section 7.09 of the within-mentioned Indenture, certifies that this
is one of the Notes referred to in the Indenture.

     Date:  May    , 2000
                ---
                              THE BANK OF NEW YORK,
                                  as Trustee

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

                                       14

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