Stop by the Connect@Sea desk on the first day of your cruise; they have a pamphlet there that walks you through how to make sure everything is turned off for your cruise. It goes step-by-step, which makes it really simple! As of my most recent cruise on the Fantasy in May 2019, iMessages (iPhone to iPhone texts) are included and you do not need to use WiFi on the ship for these messages. You just can't send pictures for free. And of course using the
DCL app on board is free too. So it should be very easy to stay in touch with the rest of your party on the ship, and if you have an iPhone, anyone back on land who also uses an iPhone. Have a great trip!
Editing to add: I believe they also have CMs who work at the Connect@Sea desk (during certain hours, not around-the-clock); they should also be able to help you with any technology needs during your vacation!