I have AT&T and before I was upgraded for free to the Canada plan, I texted when I was in Canada with my service. I just got charged for the texts at like .25 per. This dude can't text because he left his cellphone in Airplane mode, or else he is just wrong. Any American cellphone automatically goes into roamer mode when you cross the border no matter what service you have. You can see it happen on your phone as you cross the border. in my case I see the name Rogers appear on the phone.
It's really simple: cellular service providers do not make any money if they stop service. They keep service going, the phone goes into roamer mode, you get a charge for it. So as of right now I am calling a Tony on the OP. Nice try Tony. I am surprised nobody else figured this out- there is no such thing as service stopping for an American when he crosses the border, for the simple reason that it makes no sense for the cell provider to not make any money. They keep service going, the phone will roam automatically, and you get charged unless phone is on airplane mode.
Tony strikes again!