Depends on your plan. If you have unlimited data (which hardly even exists anymore), then you're pretty much fine. If you have limited data (ie. 500MB per month or something like that) then it'll be in your plan until you go over the limit, when they start charging you. If you don't have a data plan at all, then you either won't be able to get on the internet or you'll be charged a lot of cash for every minute you're on. WiFi is, of course, free. Talk to your cell provider, they'll explain it better than I did.