All I can say is my iPhone has had hit and miss coverage with the wi-fi on the RCI ships I've been on, and of course an iPod Touch is just an iPhone with no phone. Given you have to establish an internet account, log in to it, and pay for each minute you use, even if it does work well it isn't worth the hassle of dealing with the small screen, comparatively slow loading speed, and the keyboard display on the iPhone or iPod Touch. I found using my laptop or the ship's internet cafe to be much easier.
There are too many places on the islands to start listing them here. I suggest you look HERE