We admire many of T-Mobile's recent marketing tactics which have forced many of the other carriers to compete more aggressively. Would you ever switch to T-Mobile? Most visitors to this site would claim T-Mobile's coverage has too many holes to entice us away, and I would agree. But we may be wrong.
T-Mobile did not participate in the FCC auction that offered 700 MHz spectrum which provides better coverage than almost all other cellular channels. However, they did buy up quite a bit of that spectrum from others later to provide new, robust coverage in mostly rural areas. We're seeing ads for T-Mobile's, "New Extended Range" coverage...but should we believe it? I too was skeptical until I realized that T-Mobile has indeed added significant coverage in many areas using these superior 700 MHz channels. Not everyplace, but some really significant places. These are the channels given up by TV stations back in 2009 when you and I had to get a digital converter to keep our old analog TV working (I still use mine).
The only limitation to this improved coverage is that we need to use a 700 MHz device, or "4G LTE Compatible." This includes many of T-Mobile's newest phones including the iPhone 6S. Yes, that means older iPhones can't go there. But when you do go there, it's real 4G LTE, not the old HSPA. They're helping all of us by pressuring the other carriers into improving their product now that T-Mobile has checked off one more objection to their network. Coverage...what a gimmick!