I thought I heard that after a certain model, all iPhones came unlocked. Not sure if it was the 4 or 5, but might be worth confirming before you get to Negril. If it's locked, your carrier will help you unlock it for free.

We use a Blackberry curve (must be close to 10 years old now) when in Jamaica. Before I initially brought it to the Digicel store to get a SIM card, I called AT&T back home and had it unlocked (actually, I used the online chat). It's served us well for over 4 years, but on our last trip it started dropping calls/shutting down after a few minutes of talk time. I may have to unlock another phone to use on the next trip. We have an old Motorola Blackflip that might be fun.