I'll be on the Caribbean Princess a week from tomorrow and the answer I got from calling Princess is 250 minutes for $100 which works out to .40 cents a minute and thats the lowest per minute rate package they offer
Full suite guests get Free internet, but I still don't know if that would include in room Wi-Fi or in area's outside the internet cafe. (I tend to think its only free if your using their computer int he internet cafe though)
I've also heard that The Diamond members (not sure what they call them on princess though) do get a cash discount on the package internet price. Not sure how much though.