We all gave up the ability to jailbreak and tether our iPhones when we updated them to iOS 4 or purchased an iPhone 4. Hackers have been teasing us that an iOS 4 jailbreak is imminent, but now you don’t have to wait for them or the jailbreak to have tethering again. You can have tethering on your iPhone now — using an open source project hosted on GitHub called iProxy.
The only caveat is that this isn’t an easy one click solution. It is a fairly complicated one, since you will need to have or have access to a paid Apple iOS developers account so you can sign and build apps to install on an iPhone belonging to you or someone else. Developers can grab the latest copy of the iProxy source code via this tar-ball link or they can visit the iProxy project website http://wiki.github.com/tcurdt/iProxy/. Download, build, and install it on your iPhone.
Next you will find complete step-by-step instructions on the Mac OS X and iPhone setup requirements at Configuring iProxy to tether your computer to the iPhone via Wi-Fi for immediate internet access for your Macbook, iMac, etc.