Blackberry on AT&T used to be the best international deal going (maybe it still is) - you could keep your data on all the time and only get a bill for maybe $100 at the end of a cruise.
All of the cruise line execs used to use it.
I really do not understand why BlackBerry (NYSE: RIMM) has tanked as company - they still have some very positive benfits - it is just that people who rarely travel overseas all wanted the iPhone - and then the Droid (Which I got)...
But you have to turn off data roaming and still also be careful when using these phones overseas.
On cruise ships you can expect the charge to be anywhere for $2.50 to $5/minute to call out or accept a call coming in.