Hi, I need some help with the different GSM iPhoine 5 models. I'm getting my sister an iPhone 5 from ebay and she's on T-Mobile. Because I'm looking on ebay I want as many buying options as possible based on the Phone's compatibility with T-Mobile's network, so I'm looking into unlocked, AT&T and T-Mobile versions. So my questions are, 1-What's the difference between an unlocked iPhone 5, the AT&T version and the T-Mobile version (if they have a special one)? 2-What's difference, if there is any, if I use an AT&T version or an unlocked version on T-Mobile's network? 3-And finally how will I be able to tell them apart from their specs? Thank you for all your help in advance.