T-Mobile recently announced that the unlimited benefit available while roaming in Canada and Mexico is changing significantly. There are two main changes – the overall monthly data allowance has shrunk considerably, and the speeds have been dropped from LTE to 3G once you hit that limit. This is a major about-face on the feature itself, which was highly touted when the T-Mobile One Plan was rolled out a year or so ago.
I switched all of my personal lines, including the dedicated LTE connection Grace, to T-Mobile because of the T-Mobile One benefits. My main reasons for switching was cost, the improved LTE speeds and coverage around the Salish Sea and in the San Juan Islands, as well as the much higher data allowances than AT&T and Verizon. Roaming while in Canada was a secondary reason, but I still considered it when switching, and used it this last year when up in the islands and closer to Canadian towers.
AT&T and Verizon
I had used Verizon and AT&T for years prior to switching to T-Mobile. With AT&T, I had a group plan that allowed 30GB of data transfer per month for all lines, including 3 iPhones and the boat, for around $300.