It is very easy to connect using ubuntu from Nokia N81. Just follow this steps.

1. type sudo tail -f /var/log/messages at console
2. Connect the N81 with pc/laptop. You should see the log that a USB device is connected. Normally the device(N81) will connect with ttyACM0.
3. Open another console ant type:
sudo ln -s /det/ttyACM0 /dev/modem
4. then at the same console type:
pico /etc/wvdial.conf
*assume that you have pico installed.
5. Edit the file.
Phone = *99#
Username =  0
Password = 0
6. Save the file with ctrl+O
7. Type at console: