On a cruise ship presents a different unrelated situation, one I am well aware of. Avid cruiser, grand daughters have iPhones, daughter and android. Can readily test grand daughters at sea on ship wi-fi iMessage. You can't text an Android from ship on wi-fi! When you text Apple Apple you are sending it to through wi-fi to Apple servers which then send it through Apple servers to their iPhones. To text and Android phone you have to do it via SMS which require a phone service provider. YES you an do it at sea if ship has cellular at sea and you text through that. Problem is that costs you general .05 cents for every text received and .50 cents for every text sent. Photo's sent can cost $20 for each picture via cellular at sea. Sending pictures vis iPhone iMessage again wi-fi no cost.
So when I cruise I stay in touch via grand daughters and their iPhones.
When in most Caribbean ports ( Verizon anyway ) have Travel Pass turned on at via provider. This allows me to use iPhone in ports that have Travel Pass for a ONE day ( 24 hours ) charge of $10, phone, texts sending/receiving data. Check with your provider. Cellular at Sea charges 2.99 a minute for phone calls while at sea. Check with your ship what phone in cabin charges. Some charge 2.99 others only have satellite and charge fees like 8.99 a minutes with 3 minute minimums.
This is a situation that requires research with carrier BEFORE you sail.
George in NY