I think that the newer ruby red is explicitly called the SGS3 4G LTE by Samsung, originally announced for Australia and shortly thereafter for the UK.
The naming is causing confusion on both sides because here, it's just called the SGS3, same name as the one offered there originally, but with a different main processor, ram, and already 4g lte capable. (Ours have been this way since their USA debut months ago.)
And then there is the Korean variation that is quad core, lte capable.
The thing to know about the US market is that we have many radio standards for cell service, unlike the rest of the world. We all pretty much hate carrier branding but like it or not, it does signify at a glance what radios / carrier is supported.
I'm on Sprint, for example, and there's nothing you could do to your phone to make it work with my carrier. And my phone's lte radio doesn't match other American carrier lte frequencies.
Welcome to the American cell scene!
PS - so far as I recall, all of the SGS3 models here use the same battery.