I have AT&T too. We were just in Alaska in June and did a few days extra in Vancouver. The second we landed and I turned off airplane mode, I got a text asking if I wanted to opt into International Day Pass. $10/24h. Otherwise it charges per min, text, and data usage. Super clear and upfront. I turned off data whenever I wasn’t actively using it, to prolong when the next 24h period would kick in. Only applies to the phone that accepts intl day pass, not all family member phones on your plan, so it’s best to pick one person to have it and let everyone else know in advance who to contact. I had zero service at sea, but it was fine in all the ports.