There is not really an official resource for this. HowardForums.com has some information. Otherwise, you just have to ask. Some AT&T reps can see the information on where 3G is coming.
I live in Iowa and last year when i bought my iPhone i asked them about 3G.
The rep said that we, in Iowa, would have some coverage in early to mid summer, hasn't really happened. Hopefully your brother is right, we need those towers.