This would be very similar to setting up a modem dial-up.
The problems would be:
- Very different phone number
- Selecting the bluetooth device to connect through.

This page contains a small tutorial on how to do it by hand:
http://perso.club-internet.fr/olberger/btgprsfisio820orangefr.html#id2488304

The device used should be /dev/rfcommX
Section 5.2.3 explains how to do a normal GSM connection (just
requires the bluetooth device selection)
Section 5.3 explains how to create a GPRS connection (would require
both changes)

Gnome-bluetooth (included in the distribution) includes a device
chooser widget, and the ability to look up which channel needs to be
bound to the serial port for Dial-up Networking. Furthermore,
gnome-bluetooth includes Python bindings.
http://usefulinc.com/software/gnome-bluetooth