My friend told me that I could use any carriers phone as long as they use a sim card similar to my carrier, At&t. My question is what other phone carrier has sim cards identical or similar enough to at&t that I could use their phones. My old cell phone is crap now and I need a new one and most of the ones I like are from other carriers. So any help with carriers that use the same sim cards as at&t and cingular?