It used to be much easier to find these instructions online, but it took me awhile yesterday. So, here they are where I can find them, and you might be able to use them too.
These instructions work for my Blackberry Pearl on TMobile using a MacBook running Leopard. It may work with other Bluetooth-enabled phones and existing TMobile data plans, or you may find parts of the instructions helpful.
1. Pair BlackBerry and MacBook
2. Open Network Preferences
3. Select “Bluetooth” in the list of connections
4. Choose “Add Configuration…” under “Configuration” on the right side
5. Telephone Number: wap.voicestream.com
6. Account Name: guest
7. Password: guestguest
You may have to click “Apply” before being able to click “Connect.”