Apparently there is a way to enable tethering by modifying the code on the iPhone OS 3.0. If you are going to pursue this, I can only say it is at your own risk and I do not claim responsibility for what happens after. Read this whole post before getting started as there are two ways to get er’ done.
CrunchGear has a tutorial of how it works:
1. Download the carrier update from here.
2. Type this into the terminal:
– defaults write com.apple.iTunes
– carrier-testing -bool TRUE
After that start up iTunes and click the Restore button. Select the ipcc file in the disk image. After the restoration is complete, there will be an Internet Tethering option under the network section.
Another way to turn on tethering is by going to the link: http://help.benm.at/help.php on the phone browser. The steps on that website tell you how to set up and download tethering abilities through the phone.