Exhibit 10.20.3

THIRD AMENDMENT TO  CARRIER GLOBAL SERVICES AGREEMENT

THIS THIRD AMENDMENT TO CARRIER GLOBAL SERVICES AGREEMENT (hereinafter referred to as the "Third Amendment") is entered into as of the dates, set forth below, by
and between MCI WORLDCOM Communications, Inc. ("MCI WorldCom") and Universal Access, Inc. ("Customer"). For the purposes of this Third Amendment, the "Effective Date" of the rates,
discounts, charges and credits set forth herein will be the first day of the first full billing cycle following the acceptance and execution of this Third Amendment by MCI WorldCom ("Third Amendment
Effective Date").

WITNESSETH:

WHEREAS, Customer and MCI WorldCom entered into that certain Carrier Global Services Agreement signed by Customer on September 24, 1999; that certain First
Amendment to Carrier Global Services Agreement signed by Customer on May 1, 2000; and that certain Second Amendment to Carrier Global Services Agreement signed by Customer on
September 7, 2000 (collectively, the "Agreement") with respect to certain services to be provided to Customer by MCI WorldCom, as more particularly described therein; and

WHEREAS,
Customer and MCI WorldCom desire to enter into this Third Amendment for the purpose of amending the Agreement,

NOW,
THEREFORE, in consideration of the mutual promises contained herein, the parties agree as follows:

1.Definitions.All capitalized terms used herein and not expressly defined herein shall have the respective
meanings given to such terms in the Agreement.

2.Domestic Private Line Service (Option 1).Schedule One to the Agreement shall be amended by adding the
following language as a new Section 9:



3.Domestic Private Line Service (Option 1).Section 1.1 of Attachment 3-1 to the Agreement, as
amended by the Second Amendment, shall be further amended by adding the following language to the end of the section:



---

***
 Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.

---



Circuit Type

Rate per
VGE Mile

Minimum Monthly Recurring
Charge per CircuitDS-l

***

***DS-3

***

***OC-3

***

***OC-12

***

***


4.E-l Point to Point (Type 1).Section 1.2 of Attachment 3-1 to the Agreement, as amended
by the Second Amendment, shall be further amended by adding the following language as a new Section 1.2.5:



E-1 Point to Point (Type 1)Mileage

All Regions0 Mile

***1 Mile

***Each Additional Mile

***




5.New Metro Private, Line Service (Type l).Section 1.2 of Attachment 3-I to the Agreement, as
amended by the Second Amendment, shall be further amended by adding the following language as a new Section 1.2.6:



---

***
 Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.

2

---



DS-0 Point to PointILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


DS-0 EndlinkILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


DS-1 Point to PointILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


DS-1 EndlinkILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


---

***
 Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.

3

---

DS-1 HubILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


DS-3 EndlinkILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


DS-3 Point to PointILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


DS-3 HubILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


OC-3 Point to PointILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


---

***
 Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.

4

---

OC-3 EndlinkILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


OC-3 HubILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


OC-12 Point to PointILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


OC-12 EndlinkILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


OC-12 HubILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


---

***
 Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.

5

---

OC-48 Point to PointILEC

0 Mile

1 Mile

Each Additional MileAmeritech

***

***

***Verizon North

***

***

***Verizon South

***

***

***Bell South

***

***

***Pacbell

***

***

***Southwestern

***

***

***Qwest

***

***

***


6.Specific Hub Waiver.Section 1.2 of Attachment 3-1 to the Agreement, as amended by the Second
Amendment, shall be further amended by adding the following language as a new Section 1.2.7:



City

Address

Circuit ID

Order
Number

Hub Monthly
Recurring
Charge

New
EndlinksWashington, DC

1120 Vermont

o6-l lv-18l-0001

i35790

***

***New York

60 Hudson

o6-xwu-por-0004

il11011

***

***New York

601 W. 26th

o6-bj8-por-000l

ii 19520

***

***Portland

409 SW 9th St.

o6-bim-beq-0001

i2097

***

***Seattle

2001 6th Ave.

o6-sbp-sbv-0005

i8496

***

***San Francisco

200 Paul Ave.

o4-0ey-44m-000l

i18474

***

***


7.Metro Private Line Service (Type 2).Section 1 of Attachment 3-1 to the Agreement shall
be amended by adding the following language as a new Section 1.5:



---

***
 Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.

6

---



5 Year RatesDS-1 Point to points

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


DS-1 Endlinks

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


DS-3 Point to Points

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


3 Year RatesDS-1 Point to points

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


DS-1 Endlinks

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


DS-3 Point to Points

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


1 Year RatesDS-1 Point to points

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


---

***
 Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.

7

---

DS-1 Endlinks

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


DS-3 Point to Points

Bell South

Pac Bell

Verizon North

Verizon South

Ameritech

SBC

Qwest0 Mile

***

***

***

***

***

***

***1 Mile

***

***

***

***

***

***

***Each Add'l Mile

***

***

***

***

***

***

***


8.Entire Agreement.Except as expressly modified by this Third Amendment, the Agreement shall be and remain in
full force and effect in accordance with its terms and shall constitute the legal, valid, binding, and enforceable obligations of Customer and MCI WorldCom. This Third Amendment, including the
Agreement and the applicable MCI WorldCom tariffs, is the complete agreement of the parties and supersedes any prior agreements or representations, whether oral or written, with respect thereto. In
the event of a conflict between the terms of this Third Amendment and the Agreement, the terms of this Third Amendment shall govern.

9.Section References.Section titles and references used in this Third Amendment shall be without substantive
meaning or content of any kind whatsoever and are not a part of the agreements among the parties hereto evidenced hereby.

10.Acceptance.The offer created by this Third Amendment shall remain open and be capable of being accepted by
Customer until August 15, 2002. Any and all prior offers made to Customer, whether oral or written, shall be superseded by this offer. Once this Third Amendment has been fully executed, any
amendments must be in writing and signed by both parties.

IN
WITNESS WHEREOF, MCI WorldCom and Customer have caused this Third Amendment to be duly executed by their authorized representatives as of the dates set forth below, effective as of the Third
Amendment Effective Date.

|UNIVERSAL ACCESS, INC.                                    |                               | MCI WORLDCOM COMMUNICATIONS, INC.
|--------------------------------------------------------- | ----------------------------- | ---------------------------------
|                                                          |                               |                                  
|By:                                                       | /s/MARK A. DICKEY             |                                  
|Name:                                                     | Mark A. Dickey                |                                  
|Title:                                                    | SVP Procurement & Development |                                  
|Date:                                                     | 7-25-02                       |                                  
|Will/UniversalAccess/GSA3rdAmend/katherinemday/7/22/02/D8 |                               |                                  

---

***
 Certain information on this page has been omitted and filed separately with the Commission. Confidential treatment has been requested with respect to the omitted portions.

8

---

QuickLinks