Just tried for my iphone 4s, and it didn't work.
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Thank you for contacting AT&T Customer Care about unlocking your iPhone.
We cannot complete your request because we found no valid current or former
mobile or account number for this request.
If you have questions, review the general eligibility requirements for
unlocking an iPhone.
Thank you for your business. For other questions about our wireless service
or iPhones, contact AT&T Customer Care at (800) 331-0500.
Sincerely,
The AT&T Customer Care Team