We are taking a 7 day Caribbean Cruise, including stops in Puerto Rico and St Thomas, which are included in my US calling plan. How can I be sure that I am connecting to a cell tower at the port and not to the cruise ship, so I can avoid the Pay-As-You-Go rates of $2.99/minute on the ship? Do I need to be off the ship and well away from the ship to connect to land based cell towers and how will I know I'm connected to the land based cell tower and not the ship?