I want to be able to use my iphone for accessing the internet and apps etc...

My question is if I am in a wifi zone while in Negril can I use iphone without being charged anything extra? Do I need to change my settings on anything while I'm there? I can't remember but I think last time I did something to my phone on the airlplane or when I got there. I'm really bad with this kind of stuff and would appreciate some help. No time to go by ATT....