in 2000 i was able to use my nextel on board the magic at night some while sailing along the fla coast. we had a magical mystery cruise due to hurricane, so not regular itinerary. but non international plan nextel was not supported in cozumel, or freeport, so just leave the phone on board when in port, from pers exp, i lost my phone in freeport and had to buy a new one, and i couldn't use it anyway. when we were moving at night near fla coast i could call out. i think someone told me that range of antennas is around four miles.
i don't know about usvi, maybe you could check nextel site to see if they hae coverage there and if it is international only.