Consider using apps.

Check out your cruise ship's app — most major cruise lines offer one. Royal Caribbean International has a free Royal IQ app that provides all sorts of helpful info like ship maps and daily programs. For an additional $14.95, it also lets you make unlimited texts and calls to others on board who have the app — which can be especially useful on a large ship where it’s easy to lose sight of each other. Carnival Hub offers similar services for Carnival ships. You should also consider downloading messaging apps such as Signal, Viber, or WhatsApp that allow you to text, make video calls and share photos and files without racking up SMS or MMS charges (though you'll have to purchase a Wi-Fi plan onboard).

Tip: Disney Cruise Line's Navigator App features free messaging to keep in touch with others on board your cruise. You might also want to give group chat app FireChat or Jott, popular with teenagers, a spin; they work without use of a data plan or Wi-Fi connection. The catch? You have to be in close proximity to the person you're contacting.