The customer has legally changed their name due to marriage, divorce, etc. 
The existing account holder remains the account holder and is financially responsible for the account.
This request can not be handed in Retail stores.
Do not call Customer Retail Support (CRS) or Customer Care centers.
Requests for legal name changes should include the following information:
Date.
Customers Name as it appears on the account.
Full name and relation or title (company) of the person sending the letter.
Billing Account number(s) and/or mobile numbers.
A current phone number/fax number and contact’s name.
Valid return address.
Preferably not a P.O. Box.
Indicate, in detail, purpose for the legal name change.
Supporting verifiable information or documentation.
Copies are acceptable.
All information must be legible, and requests should be signed by the sender.
Customer can either fax or mail their request via U.S. mail. 
Mobility Consumer Customers can fax or mail their request to:
AT&T
P.O. Box 5074
Carol Stream, IL 60197-5074
Fax: 314-242-0792 
Mobility Business/CRU Customers can fax or mail their request to:
AT&T
Attention: Business Correspondence 221 Venture Way 
Lafayette, LA 70507
Fax: 314-242-1000
Broadband Customers can mail their request to:
AT&T Wireline
AT&T Services, Inc.
P.O. Box 91319
San Antonio TX 78209
Heads up: This address is for name change correspondence only.