Lessee ... insert brain dump here. :-)
From what I've experienced, Digital Seas seems to have the market cornered:
http://www.digitalseas.com/
Beware - it can be pricey. If you expect to require access for more than a few hours, look for a ship with an unlimited plan. For instance, I remember the Carnival Fantasy had unlimited access for about $100 in late 2001, and it was a great deal considering the alternatives.
If you have no choice but to use their kiosks, know that you'll be using just that - a Windows-based kiosk that pretty much keeps you jailed within Internet Explorer. If you absolutely must use telnet/ssh and have a web server or other browser-accessible space handy, you may consider installing an ssh applet like
http://www.mud.de/se/jta/ ... worked like a charm for me. :-D
Be prepared to pay per printed page, should you use their laser printer.
If you prefer to access from your stateroom, check in ASAP at the purser's desk once you board the ship. You may not have ethernet access and you'll have to dial-up within the ship. In that case, they usually have a limited supply of RJ11 cables and CD-ROMs you can install.
Now, actually, I avoid the software install like the plague. If you ask the admin nicely (and they have a clue ... and aren't too busy IM'ing everyone back home <LOL> - just you watch, you'll see!) you can get the dial-up info and just configure your laptop dialer solo. Sometimes you can lift this info off the CD-ROM too. :-)
One other thing about stateroom access via phone: It's usually per-minute. Any payment you make toward kiosk access usually does NOT apply. Webeat emptor!
More and more ships have 802.11b WiFi access. The reception is fine around the pool deck, the atrium/meeting areas, and some of the adjoining hallways. If you have a laptop and prefer to use that, definitely bring it - the experience will be more like using Wayport from a hotel room and, again, there's usually (but not always) a separate pricing scheme. Sometimes your kiosk access applies to it, and you'll get a popup window that shows your remaining time (which you also need to leave open). Some ships rent laptops and/or WiFi cards (PCMCIA only).
The higher category rooms and more quote-elite-unquote ships are offering (or are starting to offer) ethernet as well. Remember though, you're communicating over a maritime network. Not always the most reliable, usually kinda bursty, but it gets the job done.
What else ... don't bother with the onboard email address. Use your own via web-based access (or your laptop's email client).
Good luck, and remember, everything in moderation. <grin>