I have a T-Mobile One plan and am getting ready for a trip to Canada. I'd like to check a Canadian coverage map so I'm wondering what carrier(s) t-mobile customers use when in Canada as part of the unlimited calling in the US, Canada, and Mexico.
T-Mobile is capable of using LAC blocking to control which carrier you use in any given location. So, you may be able to roam one carrier in one location but not in another. You should just rely on T-Mobile's maps and if you are able to roam in places not shown, just be pleasantly surprised.