Well, at least this time, Florida man was not inventing new ways to break the law.
My ATT service informed me that I automatically went into overseas mode when I used the phone in Mexico. I believe that the overseas service is $100 per month (but I may be mistaken). In any case, it seems that ATT looks after its customers who forget to sign up for the overseas service before they leave.
Last time I was in Europe about 4 years ago I call AT&T and asked them if there was a plan for International travel, I was 7 countries and after that they gave a rate of $7/day for unlimited voice/text/data and every time you travelled to another country your provider listed on the phone changed
I thought this was easy and straightforward