From a previous post, I believe you said this was your first trip? Personally, I wouldn't worry about a SIM card. You will spend a lot of time figuring out if your personal phone will work on the Jamaican mobile phone networks or where you can get a cheap phone and what documentation you need to get a SIM card and phone number. I would just ask your driver if you can borrow a Jamaican phone (if you haven't booked a driver yet, try Linston in the Transport link above).

You don't need a SIM card for wifi, as many bars, restaurants and hotels have free wifi. You can just use your mobile device (in airplane mode).