(Disclaimer: this is just hearsay) I think that most cruise ships have their own cell towers, with their own roaming agreements. So if you try to connect while you're on-board, you'll be on their network and paying their rates.

Related question: does someone know how expensive is a satellite phone plan? I've seen the terminals are about $1000 a piece and they're hellishly slow but considering this kind of use in a ship or maybe in a distant place, it could be an option if the plan is not terribly expensive.

Depends on location and provider, but I worked on a remote off grid monitoring station. We uploaded about 30 gigs a month over a satellite dish. The price was comparable to cell phone, but the ping was bad. 300 ms or so, occasionally much worse.

Wow! I don't think my ADSL land line would be much better than that. The A is for asymetric, downloading is not too bad. I'm surprised it's not specially expensive. Thank you for the info!