This Article (the "How to setup Tethering via USB on Windows" section) lists simple ways to share the 3G connection from a tethered phone with other computers.
How could I do this with Ubuntu 11.04?
Assuming that you already have a computer running Ubuntu (connected to internet via 3G) and a working wifi card, the procedure to share the 3G internet with other computers is very easy.
After you connect to the internet, right click on the network manager icon on system tray and click on "Create Wireless Network." Follow the on screen instructions and connect the other computers via wifi from the network manager.
Do you have the option to use USB thethering over wifi and over bluetooth? If not you need to make sure you get that first:
sudo add-apt-repository ppa:pmcenery/ppa sudo apt-get update && sudo apt-get dist-upgrade sudo apt-get install ipheth-dkms ipheth-utils
Activate internet sharing with USB.
sudo apt-get install blueman
Activate internet sharing via bluetooth, and use blueman to pair it as an access point.