If I recall correctly, the Verizon version is the most flexible in terms of connectivity. It has more international compatible LTE bands, and it can connect to at&t's 3g network (with an at&t sim), but not at&t's LTE (4G) network. T-Mobile is a big question mark. I think the best you'll get is T-Mobile's 2g network (56kb), and even then you'll need a data plan sim; you won't be able to reuse a voice plan sim, I've tried it.