This article describes how to troubleshoot roaming problems.
INSTRUCTIONS & INFO
In order to use your device outside of the United States you must add international roaming to your account. Note: To learn more, visit the AT&T International website. Not applicable to GoPhone services.
To troubleshoot issues with roaming, from the home screen tap Settings.
Tap International Roaming.
To turn international roaming on or off, tap the International roaming switch.