For someone to contact you thru the ship costs $7 per minute. They will need to have a credit card to place the call.
Check with your carrier, but our text deal was $.05 to receive, .50 to send. Also, if you are stopping at any US ports (St. Thomas, San Juan, Key West, etc. ) most carriers have service included in you plan. That makes it a good place to turn on the phone knowing that you won't be downloading tons of junk messages.
Cellular at sea is about $2.50 per minute in addition to any charges from your carrier--again, you need to have your phone on, which means that garbage calls can come thru.
We find it easiest to give the shore to ship number to anyone necessary but to point out the cost and that it is for EMERGENCIES only. If we were to find that we needed to talk to someone, we could then call them back using cellular at sea. Honestly, unless it is a real emergency, I don't want to hear from the people back home while I'm on vacation. As harsh as it sounds, I can learn that a cousin had her baby or someone had a gall bladder out when I get home!