Call *228 from the device and when prompted select option 1 to program it.
Go to settings->general->reset-> reset network settings
Roaming data must be on – On International coverage, if prompt to turn on Roaming feature Please check the settings Settings -> General->Cellular->Cellular Data On Settings-> General-> Cellular->Roaming->Voice Roaming On and Data Roaming On
AT&T Global Customer Service 916 843 4685
– only has the apple icon on the screen.
Pressing the power and home keys for 10secs
then release
Then repeating the process for 4secs (holding power and home keys)