Download of Tether Free
With Tether Free You can activate the tethering (modem) setting on your iPhone 3G with iPhone OS 3.0 via iTunes. These Tether Free performs a console command, restarts iTunes and gives instructions for installing. Here the IPCC files are installed with the corresponding provider- identity on the iPhone.
Currently Tether Free provides only the IPCC files for O2 UK AT&T with US, but more will follow. Alternatively, you can use the iPhone Configuration Utility and the instructions on wiki to activate the tethering on the iPhone.