Exactly. Ask your neighbors/co-workers if they use ATT by you and what their experiences are.
Around Metro Detroit, ATT works ok, but not nearly as good as my Verizon service did :-/. No major issues with dropped calls or anything, mostly just a signal strength issue. I cannot recieve calls when I'm in the grocery store on ATT, but could fine on Verizon (and this is not limited to iPhone; my wife had ATT a few years back and had the same issue).