Up here in Canada, the Galaxy Note is available from the big three: Bell, Rogers, and Telus. In the United States, though, the massive phablet is exclusive to AT&T. What if you’re on T-Mobile and you want some 5.3-inch AMOLED goodness? Well, it looks like you can do that too, even if it’s a little unofficial.
The interesting thing about the AT&T version of the Samsung Galaxy Note is that it really is capable of using T-Mobile’s bands right out of the box. You just have to let it do that. In order to get the Note on Old Magenta, you need to load up a custom modem software that lets the phone latch onto those T-Mobile HSPA+ airwaves.
Naturally, the Galaxy Note must first be rooted before you can do any of this kind of tinkering and, even after that, dealing with the modem configuration files can be a little daunting for the uninitiated. If you’re willing to take that leap of faith, though, you’ll find that voice and data work just fine on T-Mobile, albeit at weaker than normal reception levels.
The full instructions can be found on XDA Developers.[Source]