The UK variant of the GS3 supports HSPA+21 (850 / 900 / 1900 / 2100), which here in the US is considered 4G. The difference between HSPA+ and LTE marketing is that HSPA+ is branded "4G" and LTE is branded "4G LTE". I'm not sure if this would work with T-Mo's 4G network, but it might work with...