I've been trying to figure this out for weeks, and finally managed to, so I' thought I'd put it up for others like me. It's country (India) and ISP (Airtel) specific, so others may not find this so useful.
This is a guide on how to connect your Mac to the Internet through your Blackberry. Bluetooth and USB both work. This works on Airtel India.
I have Mobile Office enabled, but I'm not sure whether you need this or not. Perhaps someone can try it without MO and let us know.
1. Pair your BB with the Mac using the Bluetooth Assistant. Make sure it's set to allow without asking every time.
2. Go to System Preferences > Internet and Wireless > Network.
3. Choose the Bluetooth DUN
4. The Telephone number is *99#
5. The Username is your phone number, without any 0 or country code. Eg 9829012345 (That's a random number, please don't call that!)
6. The password is the same as the username
7. Click on Advanced
8. Under Modem choose the following:
Vendor = Research in Motion
Model = Blackberry IP Modem (GSM) ((I haven't tested CDMA))
APN = airtelgprs.com
CID = 1
That's it. Click connect and you should be connected.
To connect through USB, just ignore the first step, and in Step 3, instead of choosing Bluetooth DUN, choose RIM Composite Device. The rest of the steps are the same. You'll need to install BB Desktop Manager for the Mac to have the RIM composite device show up.
APN setting on the Blackberry. I don't have this enabled, it works fine.
Hope this helps someone out there