If you do a google search, I believe AT&T puts out a list of on their corporate website that states which areas will be getting 3G.
From what I recall it doesn't give an exact timeframe, the list is more like a yearly guide that lays out their agenda of areas that they plan on expanding 3g coverage to throughout the course of the year, so just because your area is on the list doesn't mean you'll be getting 3g within 2months.