K kevincott Android Expert Sep 16, 2013 #2 AT&T is GSM/UMTS. If your GS3 uses a SIM card it should be compatible with AT&T. If your GS3 does not have a SIM card it uses CDMA and is not compatible.
AT&T is GSM/UMTS. If your GS3 uses a SIM card it should be compatible with AT&T. If your GS3 does not have a SIM card it uses CDMA and is not compatible.
