Threads like this remind me why I really don't mind Sprint.
Puerto Rico and the US Virgin Islands are part of the Sprint Nationwide Coverage.
Please go to Sprint - Nationwide Coverage
I had full 3G coverage in 2009 when I was there ... at the time I had a Blackberry and BIS worked flawlessly.
Makes me wonder if any of Sprint's prepaid services would work on either island. I don't think I have any Sprint employee friends any more, but next time I am on SprintUsers.com I will ask around. Might be good information to have for a cruiser visiting either island that must have phone contact.
Personally that's one of the things I like about sea days and places like Cozumel. I can disconnect. On my 7n cruise in 2009, the only reason I used the internet cafe was to look at my work schedule for the week I got back ...
But I ramble... :-p