Have a Samsung Evergreen but wont be able to upgrade to a newer phone till next year, was thinking of buying a smartphone off ebay or amazon. But do not know if any AT&T smartphones use sim cards.
All at&t phones have sim cards. The more newer smart phones may have a micro sim which is just a smaller sim. You could always cut your active sim or go into a at&t store and buy one which is around $15 or free if your a long time customer. Also be aware your evergreen is a basic phone which doesn't have smartphone internet and you would need to upgrade your plan too, or else they'll start charging you automatically.