While about to go to the countryside, I was desperately searching for a solution to connect to the Internet via my new Siemens S55 GPRS phone. I've searched macosxhints but could only find one for Nokia and another for Sony Erricson. After some searching on the internet, I've compiled the steps needed to make it work via my G4 Powerbook iRDA port (bluetooth should work too). You can find the instructions at BusyBee OSX in this article. FYI, I'm connected to Australia's Telstra ISP. It should work with other Australian providers and even in other countries.
For those of you with other mobile GPRS phones, you may wish to follow the link in the article to access a bunch of other mobile phone modem scripts.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030425031108623