03-03-2013 06:40:11 AM
03-04-2013 07:47:59 AM
Assuming that you are referring to the Galaxy S III since AT&T didn't sell the Galaxy 3 (which also exists), the AT&T version does not have the radio bands to pick up 4G service on most of T-Mobile's network. If you live in an area where T-Mobile has refarmed the 1900MHz band to have HSPA+ service on it, you would get 4G. It sounds like you don't live in one of those areas, so you are limited to EDGE speeds.