Iridium (the global satellite phone company) offers data access, but only supports Windows. After a fair bit of Googling, I couldn't find any data on getting it going under OS X, but I tackled it ... and it works. I've posted instructions for it, for anyone who's interested. One more thing that isn't PC-only anymore.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20041029003239706