Document:

<PAGE>

     THIS CERTIFICATE IS TRANSFERABLE IN ___________________ OR NEW YORK, NY

              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE
                               CUSIP ____________

SEE REVERSE FOR CERTAIN DEFINITIONS

      THIS CERTIFIES THAT IS THE RECORD HOLDER OF FULLY PAID AND NONASSESSABLE
SHARES OF THE COMMON STOCK, $0.001 PAR VALUE PER SHARE, OF U.S. REALTEL, INC.
transferable on the books of the Corporation by the holder hereof in person or
by duly authorized attorney upon surrender of this Certificate properly
endorsed. This Certificate is not valid until countersigned and registered by
the Transfer Agent and Registrar.

      WITNESS the facsimile seal of the Corporation and the facsimile signatures
of its duly authorized officers

      Dated: ____________

      SECRETARY                                                       PRESIDENT

COUNTERSIGNED AND REGISTERED:
La Salle National Bank
TRANSFER AGENT AND REGISTRAR

BY __________________________
AUTHORIZED SIGNATURE

<PAGE>

                                      BACK

         A statement of the powers, designations, preferences and relative,
participating, optional or other special rights of each class of stock or series
thereof and the qualifications, limitations or restrictions of such preferences
and/or rights as established, from time to time, by the Certificate of
Incorporation of the Corporation and by any certificate of designation, and the
number of shares constituting each class and series and the designations
thereof, may be obtained by the holder hereof upon request and without charge
from the Corporation at its principal office.

The following abbreviations, when used in the inscription on the face of this
certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

TEN COM - as tenants in common
TEN ENT - as tenants by the entireties
JT TEN - as joint tenants with right of survivorship and not as tenants in
         common

UNIF GIFT MIN ACT - _______________________Custodian____________________________
                          (Cust)                             (Minor)

                    under Uniform Gifts to Minors Act _______________________
                                                             (State)

UNIF TRF MIN ACT -___________________________ Custodian (until age ________)
                        (Cust)

        ________________________ under Uniform Transfers
                   (Minor)

                  to Minors Act__________________________
                                             (State)

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, ______________________ hereby sell, assign and transfer unto

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      PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE

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(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING ZIP CODE, OF ASSIGNEE)
Shares of the common stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint ___________________________________ Attorney
to transfer the said stock on the books of the within named Corporation with
full power of substitution in the premises.

Dated

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

Signature(s) Guaranteed

By: ________________________

THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (BANKS,
STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN
AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM), PURSUANT TO S.E.C. RULE 17
Ad-15. NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS
WRITTEN UPON THE FACE OF THE CERTIFICATE IN EVERY PARTICULAR, WITHOUT ALTERATION
OR ENLARGEMENT OR ANY CHANGE WHATEVER.<PAGE>

NEITHER THIS NOTE NOR ANY SECURITIES WHICH MAY BE ISSUED UPON CONVERSION HEREOF
HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR REGISTERED
OR OTHERWISE QUALIFIED UNDER ANY STATE OR OTHER SECURITIES LAW. NEITHER THIS
NOTE NOR ANY SUCH SECURITIES MAY BE SOLD OR OFFERED FOR SALE IN THE ABSENCE OF
AN EFFECTIVE REGISTRATION STATEMENT UNDER SAID ACT AND REGISTRATION OR OTHER
QUALIFICATION UNDER ANY APPLICABLE STATE OR OTHER SECURITIES LAWS, OR AN OPINION
OF COUNSEL SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION OR OTHER
QUALIFICATION IS NOT REQUIRED.

                               U.S. REALTEL, INC.

                           CONVERTIBLE PROMISSORY NOTE

Principal Amount:  $1,500,000                                September 24, 1999

     U.S. RealTel, Inc., an Illinois corporation (the "Company"), with its
principal office at 100 South Wacker Drive, Suite 850, Chicago, Illinois 60606,
for value received, promises to pay to the order of Troon & Co., and the Oliver
family trusts identified on the signature pages hereto ("Noteholder"), the
Principal Amount set forth above plus interest thereon calculated from the date
of each such advance to the Company until paid at the annual rate of seven
percent (7%), compounded annually. Interest accrued hereunder shall be due and
payable in lawful money of the United States on March 30, 2000 and on the
Maturity Date and principal hereunder will be due and payable in lawful money of
the United States in full on the first anniversary of the date hereof (the
"Maturity Date"), unless this Note shall have been previously converted pursuant
to Section 2 hereof, in which case all outstanding principal under this Note
shall be satisfied in full by virtue of such conversion and the issuance and
delivery of fully paid and non-assessable shares of Conversion Stock to the
Holder of this Note as set forth in Section 2 hereof and all accrued interest
thereon will be due and payable in lawful money of the United States at the time
of such conversion. This Note is not prepayable or redeemable by the Company
prior to the Maturity Date. Principal and interest not paid when due shall bear
interest at twelve percent (12%) per annum as of the due date and shall be
payable on demand. Payments by the Company shall be applied first to any and all
accrued interest through the payment date and second to the principal remaining
due hereunder or upon conversion hereof.

     The following is a statement of the rights of the holder of this Note and
the conditions to which this Note is subject, and to which the holder hereof, by
the acceptance of this Note, agrees:

     1.   DEFINITIONS. As used in this Note, the following terms, unless the
context otherwise requires, have the following meanings:

          1.1. "COMPANY" includes any corporation or other entity which shall
succeed to or assume the obligations of the Company under this Note.

<PAGE>

          1.2. "COMPANY COMMON STOCK" shall mean the Company's Common Stock, par
value $.001 per share.

          1.3. "CONVERSION STOCK" shall mean the Company's Common Stock or
RealTel de Argentina Stock Common Stock, as elected by the Noteholder at the
time of conversion.

          1.4. "CONVERSION PRICE" shall mean (a) for the RealTel de Argentina
Common Stock , an amount equal to the principal amount of this Note divided by
the number of shares of RealTel de Argentina Common Stock which shall result in
the Noteholder owning 9% of the total shares of RealTel de Argentina issued and
outstanding at the date of conversion and (b) for the Company Common Stock (i)
the lowest price per share paid for the Company Common Stock or other security
convertible into common stock purchased from and after the date hereof in a
Financing or (ii) if no Financing shall have occurred, the value per share of
the Company Common Stock as determined in good faith by the Company and
Noteholder and, if no such determination is made within ten (10) business days
following Noteholder's request for a valuation, then each of the Company and
Noteholder within forty five (45) days thereafter (the "APPOINTMENT DATE"),
shall designate an independent appraiser, knowledgeable and experienced in
valuing businesses of a type similar to the Company, and each such appraiser,
within twenty (20) days after the Appointment Date shall jointly choose a third
qualified independent appraiser, provided that if either party shall fail to
choose a qualified independent appraiser, within the time prescribed, the
independent appraiser chosen by the other party shall be entitled to designate
itself as the third appraiser. Within thirty (30) days following its
designation, the third appraiser will deliver its determination of the Value of
the Company Common at the Valuation Date. The foregoing determination shall be
final and binding upon the parties hereto and the expenses of the appraisers
will be paid one-half by each party.

          1.5. "FINANCING" shall mean the Company's sale, from and after the
date hereof, of common stock or any other security convertible into common stock
for cash capital and/or retirement of debt securities (excluding securities
issued pursuant to option plans, outstanding options, securities issued upon
exercise of outstanding options and this Note and other notes of substantially
identical terms) in one transaction or a series of transactions occurring after
the date hereof.

          1.6. "NOTE" shall mean this Convertible Promissory Note.

          1.7. "NOTEHOLDER", "HOLDER", or similar terms, when the context refers
to a holder of this Note, shall mean any person who shall at the time be the
registered holder of this Note.

          1.8. "REALTEL DE ARGENTINA" shall mean RealTel de Argentina SA.

          1.9. "REALTEL DE ARGENTINA COMMON STOCK" shall mean Common Stock,
$1.00 par value per share, of RealTel de Argentina.

          1.10. "REALTEL DE ARGENTINA SHAREHOLDERS' AGREEMENT" shall mean that
certain Shareholders' Agreement dated as of July 25, 1999, by and among the
Company, Access Financial Group, Inc., Mark J. Grant, Pablo Hoffmann, Gabriel
Melzi, Raul Melzi, Flavia Melzi and RealTel de Argentina.

                                       2
<PAGE>

     2.   CONVERSION.

          2.1. VOLUNTARY CONVERSION. At any time on or after January 1, 2000
until the date this Note is paid in full, the Noteholder will have the right to
convert all but not less than all of the outstanding principal on this Note into
Conversion Stock at the Conversion Price. Conversion as described in this
Section 2.1 shall occur only upon surrender of this Note for conversion at the
principal office of the Company, accompanied by written notice of election to
convert in the form of EXHIBIT A hereto, which notice shall specify whether the
conversion is for Company Common Stock or RealTel de Argentina Common Stock and
shall be delivered no later than thirty (30) days prior to the Maturity Date.

          2.2. NO FRACTIONAL SHARES. No fractional shares will be issued on
conversion of this Note. If on any conversion of this Note a fraction of a share
results, the Company will pay the cash value of that fractional share,
calculated on the basis of the applicable Conversion Price.

          2.3. RESERVATION OF STOCK. The Company has taken all necessary
corporate action and obtained all necessary consents and approvals to authorize
the issuance of this Note, and as of the closing of a conversion of this Note
will take all necessary corporate action, will cause RealTel de Argentina to
take and will obtain and will cause RealTel de Argentina to obtain all necessary
consents and approvals to authorize the issuance or transfer of the shares of
Conversion Stock upon the conversion of this Note pursuant to Section 2.1 above.

          2.4. FULLY PAID SHARES; CERTIFICATES. All shares of Conversion Stock
issued or transferred upon the conversion of this Note shall be validly issued,
fully paid, non-assessable and free and clear of any claims, liens or
encumbrances. The certificates representing the shares of Conversion Stock
issued upon conversion hereof shall be delivered to the Noteholder against
surrender of this Note.

          2.5. CERTAIN REPRESENTATIONS. The Company represents and warrants to
Noteholder that (a) there are no restrictions, either at law or by agreement,
including, without limitation, the RealTel de Argentina Shareholders' Agreement,
preventing the transfer of the RealTel de Argentina Common Stock from the
Company to the Noteholder pursuant to the terms and conditions hereof and (b)
attached hereto is a true and accurate list of the current shareholders of
RealTel de Argentina and their ownership interests.

          2.6. NO RIGHTS OR LIABILITIES AS SHAREHOLDER. This Note does not by
itself entitle the Noteholder to any voting rights or other rights as a
shareholder of the Company or RealTel de Argentina. In the absence of conversion
of this Note, no provisions of this Note, and no enumeration herein of the
rights or privileges of the holder shall cause such holder to be a shareholder
of the Company or RealTel de Argentina for any purpose by virtue hereof.

          2.7. RIGHTS UPON A FINANCING. The Company shall provide the Noteholder
with prior written notice of a proposed Financing, such notice to set forth in
reasonable detail the parties, the principal terms and the anticipated closing
date thereof.

     3.   REALTEL DE ARGENTINA SHAREHOLDERS' AGREEMENT. In the event that
Noteholder elects to convert this Note into RealTel de Argentina Common Stock,
the Noteholder agrees to

                                       3
<PAGE>

execute a counterpart copy of and become a "Shareholder" pursuant to the RealTel
de Argentina Shareholders' Agreement.

     4.   AMENDMENT TO THE REGISTRATION RIGHTS AGREEMENT AND THE SHAREHOLDERS'
AGREEMENT. Contemporaneously herewith, the Company shall deliver to Noteholder
(a) an amendment to that certain Registration Rights Agreement dated October 2,
1998 among the Company and certain of its shareholders so that the shares of the
Company Common Stock issued upon conversion shall become "Registrable Shares"
thereunder when such shares are converted pursuant to the terms of this Note and
(b) an Amendment to that certain Shareholders' Agreement dated October 2, 1998
among the Company and certain of its shareholders which shall add Troon & Co.,
as a "Shareholder" pursuant thereto.

     5.   WAIVERS. The Company waives presentment, demand for performance,
notice of nonperformance, protest, notice of protest, and notice of dishonor. No
delay on the part of the Noteholder in exercising any right hereunder shall
operate as a waiver of such right under this Note.

     6.   EVENTS OF DEFAULT. The Company shall be in default under this Note if
any payment of principal or interest is not paid within ten (10) business days
of when the same is due and payable. If an event of default shall occur and be
continuing, the entire principal amount of this Note, together with the accrued
interest, shall become and be immediately due and payable, without presentment,
demand, protest or notice of any kind.

     7.   COLLECTION. If the indebtedness represented by this Note or any part
thereof is collected at law or in equity or in bankruptcy, receivership or other
judicial proceedings or if this Note is placed in the hands of attorneys for
collection after default, the Company agrees to pay, in addition to the
principal and interest payable hereon, reasonable attorneys' fees and costs
incurred by the Noteholder.

     8.   USURY SAVINGS CLAUSE. The Company and the Noteholder intend to comply
at all times with applicable usury laws. If at any time such laws would render
usurious any amounts due under this Note under applicable law, then it is the
Company's and the Noteholder's express intention that the Company not be
required to pay interest on this Note at a rate in excess of the maximum lawful
rate, that the provisions of this Section 6 shall control over all other
provisions of this Note which may be in apparent conflict hereunder, that such
excess amount shall be immediately credited to the principal balance of this
Note (or, if this Note has been fully paid, refunded by the Noteholder to the
Company), and the provisions hereof shall be immediately reformed and the
amounts thereafter decreased, so as to comply with the then applicable usury
law, but so as to permit the recovery of the fullest amount otherwise due under
this Note.

     9.   GENERAL PROVISIONS.

          9.1. NOTICES. Any notice, request or other communication required or
permitted hereunder shall be in writing and shall be deemed to have been duly
given if personally delivered or mailed by certified mail return receipt
requested, postage prepaid, at the respective addresses of the parties as set
forth on the first page hereof. Any party hereto may change such address by
notice hereunder. Notice shall conclusively be deemed to have been given when

                                       4
<PAGE>

personally delivered or when deposited in the mail in the manner set forth above
and shall be deemed to have been received when delivered.

          9.2. SEVERABILITY; HEADINGS. In case any provision of this Note shall
be declared by a court to be invalid, illegal or unenforceable, the validity,
legality and enforceability of the remaining provisions shall not in any way be
effected or impaired thereby, unless to do so would deprive the Noteholder or
the Company of a substantial part of its bargain. Such court may reform such
invalid, illegal or unenforceable provision so as to give the maximum
permissible effect to the intentions of the parties as expressed in this Note.
All headings used herein are used for convenience only and shall not be used to
construe or interpret this Note.

          9.3. ENTIRE AGREEMENT; CHANGES. This Note and the Subscription
Agreement between the Company and Noteholder of even date herewith contains the
entire agreement between the parties hereto superseding and replacing any prior
agreement or understanding relating to the subject matter hereof. Neither this
Note nor any term hereof may be changed, waived, discharged or terminated orally
but only by an instrument in writing signed by the party against which
enforcement of the change, waiver, discharge or termination is sought.

          9.4. LAW GOVERNING. This Note shall be construed and enforced in
accordance with, and governed by, the internal laws of the State of Illinois,
excluding that body of law applicable to conflicts of law.

          9.5. LEGAL FEES. The Company shall pay the reasonable legal fees of
the Noteholder in an amount not in excess of $5,000 in connection with the
negotiation and execution of this Note and the related Subscription Agreement
and other documents executed pursuant hereto.

          9.6. SPECIFIC PERFORMANCE. The Company and Noteholder agree that it is
impossible to measure in money damages which will accrue to Noteholder by reason
of a failure of the Company to allow a conversion to Conversion Stock pursuant
to the terms hereof. Therefore, if Noteholder shall institute any action or
proceeding to enforce the provisions hereof relating to such conversion, the
Company hereby waives the claim or defense therein that there is an adequate
remedy at law.

          9.7. ALLOCATION. The Noteholder shall have the right to allocate among
themselves all or any portion of the Conversion Stock by so designating to the
Company at the time the written notice of election to convert is provided to the
Company pursuant to Section 2.1.

          9.8. AGENT. The Noteholder hereby appoints Troon & Co. as agent (the
"Agent") hereunder to act on their behalf for all purposes hereunder. The
Company shall be entitled to rely on the direction of the Agent for all purposes
hereunder, including, without limitation, exercise of the conversion right
pursuant to Section 2 of this Note.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       5
<PAGE>

IN WITNESS WHEREOF, each party has caused this Note to be signed in its name
this 24th day of September, 1999.

THE COMPANY:                           U.S. REALTEL, INC.

                                       By: /s/ Perry H. Ruda
                                          -------------------------------------
                                       Name:  Perry H. Ruda
                                            -----------------------------------
                                       Title:  Chairman
                                             ----------------------------------

NOTEHOLDER:                            TROON & CO.

                                       By:  /s/ Ross J. Mangano
                                          -------------------------------------
                                           Ross J. Mangano, Trustee & Partner

NOTEHOLDER:                            JOSEPH D. OLIVER TRUST
                                       GO CUNNINGHAM TRUST

                                       By:  /s/ Ross J. Mangano
                                          -------------------------------------
                                           Ross J. Mangano, Trustee

NOTEHOLDER:                            JOSEPH D. OLIVER TRUST
                                       JAMES OLIVER II TRUST

                                       By:  /s/ Ross J. Mangano
                                          -------------------------------------
                                           Ross J. Mangano, Trustee

NOTEHOLDER:                            JOSEPH D. OLIVER TRUST
                                       JOSEPH D. OLIVER, JR., TRUST

                                       By:  /s/ Ross J. Mangano
                                          -------------------------------------
                                           Ross J. Mangano, Trustee

NOTEHOLDER:                            JOSEPH D. OLIVER TRUST
                                       SUSAN C. OLIVER TRUST

                                       By:  /s/ Ross J. Mangano
                                          -------------------------------------
                                           Ross J. Mangano, Trustee

                                       6
<PAGE>

                                    EXHIBIT A

                    (Form of conversion notice to be executed
                by the Noteholder at the time of the conversion)

To U.S. RealTel, Inc.:

     The undersigned, holder of that certain Convertible Promissory Note in the
principal amount of $1,500,000 dated September ___, 1999, issued by U.S.
RealTel, Inc. (the "NOTE"), hereby exercises its right to convert all principal
and accrued but unpaid interest of said Note into ______ shares of Common Stock
of [U.S. RealTel, Inc./RealTel de Argentina - specify one or the other] at the
Conversion Price established pursuant to the terms of the Note.

            Please issue the certificate for the shares as follows:

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                               Print or Type Name

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                   Social Security or Other Identifying Number

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                                 Street Address

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City                         State                             Zip Code

and deliver it to the above address, unless a different address is indicated
below.

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

                                             By:
                                                -------------------------------
                                                  Name:
                                                       ------------------------
                                                  Title:
                                                        -----------------------
Dated:______________
                                             (Signature must conform in all
                                             respects to name of holder as
                                             specified on the face of the Note
                                             or, if the Note has been
                                             transferred without reissuance by
                                             the Company, the registered
                                             holder's name as specified in the
                                             Company's records)

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