In the US... on AT&T:
First:https://www.att.com/deviceunlock/client/en_US/
Then get response e-mail:
Request number: XXXXXXXXXXXXXXXXXXXXXXXXX
Thank you for contacting AT&T Customer Care about unlocking your AT&T Mobile device.
We have reviewed your request and confirmed that the device may be unlocked.
Please allow 24 hours upon receipt of this notification to complete the unlock process.
To complete the unlock, simply
1. Open iTunes on your Mac or PC and verify that you have Internet connectivity.
2. Ensure a SIM card is inserted into your iPhone.
3. Connect your iPhone using the dock connector to USB cable that came with your iPhone.
4. Backup and restore your iPhone using iTunes. For information on backup and restore, please visit http://support.apple.com/kb/HT1414.
5. After restoring, your iPhone will be unlocked.
Additional information on unlocking can be found at http://support.apple.com/kb/TS3198
For questions regarding AT&T Mobile device, please visit the Phone/Device Learning Center.
Thank you for your business. For other questions about our AT&T wireless service or other Mobile devices, please visit att.com.
Sincerely,
AT&T Customer Care Team
DO NOT REPLY TO THIS MESSAGE
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Once you've followed the instructions this is what you'll see:
followed by
then
finally
and you're done!
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IF THE PHONE HAS SPACE PROBLEMS AND IT WILL NOT RELOAD THE BACKUP FILE, ERASE YOUR PHONE. You're going to use the backup you created anyway...