Here is my experience: I have a VX8300 with a normal voice-only plan. Previously, every time I tried to do DUN over Bluetooth, it would hang up after a few seconds. I had Googled and Googled for a fix, but no luck.

Then added the supplementary AT command "AT$QCMDR=2", and QNC dial-up networking started functioning properly. (I also did a one-time entry of "##dialup" on the keypad, which is one of the folk remedies for enabling DUN over Bluetooth.)

In summary, my settings are:

Connection type "Data Call"
Dial-up number "#777"
User name "qnc"
Password "qnc"
Supplementary AT command "AT$QCMDR=2"

The QNC dialup is pathetically slow, but at least it's free (except for the airtime minutes).

My wife's Verizon phone (an older Motorola model) will do Bluetooth QNC DUN without any special AT commands.

Doug