Same here. We use texting. Turn off the data on your phone. Texts cost 50 cents to send , 5 cents to received on the ship. Have anyone you need to keep in touch with text you if they need you. Then you can respond if needed. The downside of this is that your phone will receive calls. You can turn your ringer off and not disturb anyone. Just don't answer and you won't get charged for the phone call. (And if you do need to talk with the person you can text them back to find out if they REALLY need you to call.
For Data... no luck. Unless you are on a cruise line that offers internet packages. You can set you phone up for Wifi and use your data package. Then turn the data roaming off and the wifi on when you want to "sync" you email and such. Just be really careful doing this as to not leave the data on and turn the wifi off (it might use the cellular at sea data roaming @ $20 for 20 MByte.... Last time we brought a tablet computer that ONLY has wifi. So you can buy the data package and simply turn the wifi on and off to sync. That way you can throttle the data usage as needed.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007