It's called tethering, and the two websites you should look at:
- http://www.taniwha.org.uk/
- http://www.fibble.org/archives/000508.html
The BlackBerry Modem Scripts found on both sites are essentially the same (diff). I won't bore you with the details, but just follow those instructions... and you'll like getting internet wherever you go. I just have two things to iron out: I get disconnected after a few minutes of inactivity, and I get a "Bluetooth Model Resource Busy" error after I've uploaded pictures from my phone to the Mac. For the former, I just reconnect; To get around latter, I have to go through the stupid process of repairing my device and setting it all up again. :(
In fact, I wrote this post over the thether. :)