Magnetic asked me to post this tutorial on PPCZone for those in similar conditions, all i did was to follow a tutorial online (in italian) meant for average PC users.
USB phone->PC cable
Ubuntu Breezy (5.10)
1) Create a file called "wvdial.conf" in /etc/ with a plain text editor (gedit did the job for me) with the following content:
Modem = /dev/ttyUSB0
Baud = 460800
Init1 = ATZ
Init2 = AT+CGDCONT=1,"IP","internet.wind",,0,0
ISDN = 0
Modem Type = Analog Modem
Carrier Check = no
Phone = *99#
Username = ''
Password = ''
In the Init2 string change "internet.wind" to the access point string of your mobile operator.
2) Remember to configure your mobile for GPRS/UMTS services (follow their instructions) and to activate the service itself.
3) If you have connected in the past to ADSL from your Pegasos using Linux remember to do following:
a) open the Terminal;
b) type "network-admin" and give your root password when asked;
c) disable ethernet connection or you won't be able to go online using your mobile as a modem;
4) open the Terminal and type:
Now you should be online :).
P.S.: I did it using a tutorial this summer, i'm not sure I've written everything, your mileage may vary, comments and corrections are welcome!