First of all, thank you for posting these instructions.
They helped me setting up the GPRS connection from my raspberry pi tremendously! 🙂
One question though...
You mentioned at the beginning of your post that a powered USB hub has to be used.
I plugged the Huawei Vodafone modem directly into the USB slot of the RPi (without the powered USB hub) and it works fine. It successfully connects to the internet and I'm able to do all the browsing and stuff.
Since I'm using the latest revision of the RPi (rev 2, the one made in the U.K., bought in september 2012), have you perhaps heard if the USB powering problem has been fixed for that revision? Or is it possible that I'll will be experiencing the random dropping of my GPRS connection?