AT&T Iphone and a US Cellular sim card?

I'm really interested in the Iphone and I know that the AT&T Iphone has a space for a sim card. (US Cellular is the best carrier where I'm from) Does anyone know if it is possible to purchase a US Cellular sim card and put it into an AT&T Iphone?

It could work depending on alot of things, because I know that's what I did. If the phone is unlocked (open to other carriers) than sure, it has to. If it's not you can always unlock it, unless the phone is stolen or owes money to another company, which I'm sure isn't the case. (just thought I should mention) Give it a try, the cheapest sim cards are usually found on ebay. If your skeptical, you can always find the answer online from other people's expierence. Hope this helps.