We'll I am not sure if your dongle works or not, or even if your phone supports Dial-Up Networking over BT, however below is the general way its done.
First Download
bluez and compile it and install it.. then follow the following steps.
Code:
1. /sbin/modprobe rfcomm
/sbin/modprobe bnep
/sbin/modprobe sco
/sbin/modprobe l2cap
hcid
sdpd
hciconfig hci0 piscan noauth up
2. hcitool scan
You'll get something like this:
Scanning ...
00:12:68:15:E5:09 P910i
3. sdptool browse 00:12:68:15:E5:09
Use the same address your got above
You'll get a list of options find the service name Dial-up Networking
and Read its channel for me it was 7.
4. rfcomm bind 0 00:12:68:15:E5:09 (Address above) 7 (Channel)
5. you may use kppp as your dialer and use /dev/rfcomm0 as your modem.
Please let me know if you need futhure help.