Many AT&T phones are incompatible with the "pay-as-you-go" or "GoPhone" service. As of 2015, phones that do not have 4G/LTE cannot make use of the service, and Blackberry cellular devices are also exempt.
It is possible to use any iPhone or 4G/LTE device other than a Blackberry as a GoPhone, as long as the device is not under any previous contract. Most smartphones are compatible with this service, regardless of brand, provided they are unlocked or otherwise free from prior contracts.
GoPhone services include Wi-Fi (data only, including AT&T Wi-Fi hot spots), text, picture and video messaging, and voicemail. Similar services are available from other suppliers, such as T-Mobile's Pay As You Go.