United States
From Droam Prepaid SIM Encyclopedia
I'm guessing that this is horribly out of date because Cingular was dropped in favor the name ATT Wireless in 2007. You can refer to the official press release from them about this below. It's dated January, 2007. www.att.com/gen/press-room?pid=4800&cdvn=news&newsarticleid=23308