Lisa is thinking about changing mobile phone plans from AT&T to T-Mobile because her phone didn't do well while on a cruise and they charged her $300. Leo says that no phone plan works while you're at sea. Only when you're in port. Leo says that Lisa may have been using Cellular at Sea, and you don't want to use that because it's very expensive. You also want to be sure to turn off data roaming. Airplane mode is even better.