Hi there puzzlers - have a go at this one - suggest an answer but DON'T give your method (I want to keep people guessing for a bit) - I'll post the solution in a few days time!
I used CC several years ago. Sim card was T-Mobile. Went to visit family in Alaska. T-Mobile does not work there. I had to go to a Sears store and buy a AT&T sim card. Once I returned to CONUS, I left CC like a hot potato.