Most US cell phones can be unlocked via the web for a small fee. The best place will depend on the phone you want to unlock. You can purchase unlocked phones from amazon in the $35 range. IPhones are a definite exception. IPhone 4s must be baseband/modem version/firmware 1.59 to unlock. I purchased a Jamaican Lime SIM card from mrsimcard with unlimited data for 7 days for $59.00. They also have cheap calling plans to the US. Most of their plans are for short stays like a week. If you are staying longer you might be better purchasing it Jamaica. They will activate you SIM 2 days prior to travel, so that you can test you Jamaica number before you leave the States. (To test you just call it, but don’t answer it).