Their data does get a little flaky the when out of fairly populated areas, but I have seen this improving very quickly and can make many long drives with full data coverage.
I don't know, I think it might just be marketing.
I took the Empire Builder recently, which basically skitters along the Northern border from Chicago to Seattle/Portland, and T-Mo coverage was nil for the bulk of the trip. Can't say I really minded, though.
Usually coverage is fine.
You're correct though, around my city and most cities I've been too domestically, I've found the coverage to be pretty good. Either way, the cost and ease have kept me on their program even with the occasional coverage gaps. But somebody routinely out for non-metro trips might not like it.
However, I would never go back to ATT/VZ absent a major change in their behavior. Happy TMO customer.
I also have some pretty bad coverage when I go up to Vermont.
So, if you stay in the cities. Excellent Coverage. Roam into the rural world: Spotty coverage.
Fact, though, even AT&T's coverage in some of these same locations is pretty poor. Verizon seems to work best.
In my area (Santa Cruz, CA) tmo are weak. Heck I barely get coverage in my house, and walking along West Cliff drive has sections with no coverage. Verizon is strong.
However I very rarely actually use the phone as a phone so I mostly don't care.
The places where coverage hasn't been a problem: anywhere else.
The only places I don't have coverage are usually the places I go to get away from phones/internet so I don't mind too much.