I previously described how to PPP over GPRS via Bluetooth to a Sony-Ericsson K family mobile modem. With my previous K700i, using Dapper (I didn’t try with Edgy), talking to the modem via USB was very simple because the modem was reachable at /dev/ttyUSB0: the modem of my new K800i is reachable at /dev/ttyACM0 (I suppose that this switch is due to the changes made in Edgy/Feisty and that it is not on the K family side).
Using this new device, you can call pppd using this script.
[...] It immediately worked with the graphical tool Ubuntu provides for wired/wireless/dialup networks: unfortunately, when I installed the driver shipped with it, it stopped working properly. Of course I was still able to talk with it using pppd (the modem is reachable at /dev/ttyUSB0) as I previously described. [...]