I'm speaking from a hardware perspective. It supports the 850 and 1900 network bands that AT&T uses, but will it work? The phone is amazing, absolutely destroys the Inspire 4G (which is a complete joke in my opinion).
No. It's a CDMA phone using 800 and 1900 mhz bands. CDMA phones can't be used on GSM networks (AT&T, Tmobile...). GSM and CDMA are completely different technologies.