Based on the stats that Apple provided, the AT&T version has the same CDMA radios as Verizon and Sprint. However, as KPOM mentioned, they might give you a hard time for bringing this version of the phone to their network (they might think it's GSM only). In any case, you should still be able to use it.
The only way you can buy it is if you have or are getting new service with AT&T. They'll sell you the phone so long as they provide the registered SIM with AT&T. I've heard some people are just getting it, then cancelling their service.