There is no AT&T 3G in Wyoming and Montana. There also isn't any EDGE really. My iPhone dropped down to the "o" (whatever that is btw) and speeds were totally gongshow. Main reason why everybody has Verizon in those states. I live in Colorado so I have 3G coverage where I am, but anywhere in the mountains, it's all EDGE, but my friend gets 3G coverage where he live in the mountains with Verizon.
That "o" is GPRS. So yes, it is expected to be *very* slow.