You might want to check which system the island is set up for. Cingular uses a different system from Verizon, for example. Phones can be "unlocked" to accept local SIMs, and will be cheaper to operate with a local SIM, but they need to be compatable with the local network.
its like vonage, but allows you to have an international call forwrading number. by international i dont mean phone numbers that dont fit the traditional 10 digit. Carribbean numbers are 1-XXX-XXX-XXXX just like US numbers, i bought a cheap phone down here, incoming calls are free, out going calls are around 50-60cents/min, so calls to me are free and my family dials a local number.
When I lived in St. Maarten I was burning up $1.95/min by buying phone cards calling the states. Some other students and myself split the cost of the best wireless internet package the internet company had to offer and I set up the vonage account and it worked as good as gold. I could call anyone in the states and international rates were as cheap as dirt. Hope this helps.