You need to check with your provider for more detail. What ports are you talking about? When I was in the Caribbean mine had extended service in Puerto Rico (no charge), but in St Thomas had a roaming fee. While at sea it didn't have service. I have Verizon.
In time most ships will offer cell service at sea but the cost will be prohibitive. It cost me $5 on our last Princess cruise to listen to a short voice mail. It'll be OK for emergencies but not to chat for any period of time about the weather.
I guess where I'm going with this and I think the GURU probably answered it.
We will be traveling with a couple that won't be with us 24/7, so we'll need to contact them in most any given situation i.e. ship to shore, shore to shore, within the ship. I've read about walkie-talkies you can rent from the ship services but don't hear much from anyone on the chat-lines. I'm not a cell-head; don't need the silly things except for emergencies but was thinking they might provide a means of comm in the event we four needed to contact.
The frs/grms walkie talkies are OK in a pinch but don't expect them to give a reliable contact all the time. Depending on what deck you & the receiving party is on it may work sporadically at best. Don't count on ship to shore communications unless the person is standing at the tender pier & the other is on deck. The advertized ranges are extremely overrated to the point I can't believe they get away with the exaggerations. Sometimes their more trouble than their worth but if you do decide to go that route, buy you own & don't rent them. With what you'll pay for rental will be far more than buying them outright. Do a search for radios & you'll find plenty of discussions about their use.
Understood....How about cell phones? I realize at sea, they're probably worthless, unless their signal is from satelite. But near or in ports, can you communicate off and on the boat with those that receive signals from towers?
If the ship has a cell phone system installed & is near a port they turn it off & you can then use the cell system from land. On the ships system you'll notice that you roaming. The ships extra charges varies form what I read but on our last trip on the Grand Princess I checked my voice mail (thinking we were close enough to land) & incurred a $2.50 per minute charge. (Verizon). If you use the ships service to call another Verizon for which there would normally be no charge (from Verizon) the ship still gets $2.50 per minute for use of their equipment. If you call another cell provider you'll incur the $2.50 per minute for the ship + the normal charge from you carrier for cell service. The charges will show up on you bill from you provider about a month later & they reimburse the cruise line. I suppose if it's a quick call to locate someone it might be worth the cost. Not all ships have the cell equipment installed yet. My provider does have coverage in Puerto Rico & Hawaii which doesn't cost me any extra for roaming but for most of the islands in the Caribbean I get billed roaming charges.