Oh i thought those were called "cellphone"
So how can I get a smartphone if I'm outside of AT&T's market?
I guess I'll go to a shop, ask for a smartphone and go to a phone company and ask for a phone&data plan....
But in your example, why would I buy a phone from AT&T if I'm going to get a GoPhone sim? Won't I be paying for two phone plans then? AT&T (unused, but still per month costs) and GoWhatever?