dont know if there is a difference, factory unlocked, works everywhere i would assume
If it's factory unlocked it's not a US version. Does it say a model number? GT-I9300 is international, SGH-T999 is T-Mobile, SGH-I747 is AT&T, SCH-I535 is Verizon, and SPH-L710 is Sprint. There are some differences, and it looks like the international version is probably the worst (see
here - click 'show' to view the comparison table), but it's basically the same phone. You should be able to use the international version in the US on T-Mobile and AT&T, but the data will be slower than the carrier specific versions.