I have readt that AT&T also works in St. Thomas. I'd expect a lot do as they are a US virgin island. Also remember Key West is part of the US, even though it does seem so removed. Also been some reports of service on CC.
Some of these newer phones can pick up better, but once the ship is out on the ocean, there will really be no cell service to speak of unless you have a sattelite phone.
You're best looking up the website for your cell provider, they will have the most up to dat info.
I'm personally of the put it in a drawer and not look at it again till we return to port kind of person.
I just give people back home the number to call the ship, if some emergency happens back at home.
1 888-dc-at-sea (322-8732)