I have AT&T and that same issue when I go to Belle Isle or too far out on the pier at Pier Park. An easy is to fix it is call up AT&T, ask for the retentions department and ask to be placed on the Roam North America package. It is free and gives you unlimited talk & text in Canada and something like 1 GB of data. You have to go through retentions though, since normal sales associates don't seem to know about it. It is seriously great--especially if you travel to Canada frequently.
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