I was able to get BT DUN working using my 8830 (Bell Canada) and my N800. The N800 has the lastest firmware update and the 8830 is on version 4.2.2.123.

On the N800 side, I used the GPRS option, checked the "trusted device" option, dial-up number is #777, username is bell1X, and password is the 4 digit voicemail access code. Everything else was at the default settings.

I didn't have to do anything on the 8830 side - just made sure that the 2 devices were paired up.

I had a Blackberry 7250 before and was never able to make it work.

Also had no problems getting the BT DUN working between the 8830 and my Sony T250P laptop.

Hope that helps.