For visitors to Negril, or anywhere for that matter, common sense should prevail. I have stated ways not to make your self a "mark" and it is simple common sense you should apply where ever you are.
In the years living here, this topic does come up from time to time in casual conversation. An iPhone does not make you a "mark". The cellphone shop owners in Negril tend to have an instinct when an iPhone is stolen. If the "customer" asks to make it usable, they charge between us$300 to $400 for that service depending on the model. That alone deters people from stealing iPhones, they will not be able to sell the phone to make any profit.
These are the facts. Enjoy Jamaica and use your iPhone as you see fit. Use the same caution you would use anywhere.