No, you don't. Put your phone in airplane mode, and there is free wifi to use for the app. The app includes a chat function to text with people on the ship, has all the menus for the whole trip, all the activities for the whole trip--so you can see all the days/times an activity is happening and you can favorite the ones you're interested in. While I loved the paper navigator, especially to bring home, the app has so much more.