Last week Musclenerd released two bsdiff patches to patch the CommCenter of your 3.1.2 iPhone 3G, 3GS to enable Internet tethering. Patching the CommCenter is for advanced users only and it requires Mac OS, Terminal knowledge and Time. Thanks to Andre Sendowski to release the Cydia package for enabling the Tethering for iPhone 3G/3GS firmware 3.1.2 The process is as easy as 1-2-3 you needn’t to purchase like Wi App (9.95$) Just fire the Cydia and follow the following steps.
Step 1. First start Cydia and add "iphone-notes” Repo with following.
Update : If you adding the repo throws an error then simply search iphone-notes and the repo package will appear to install itself.
Step 2. Now search for "tethering 3G – 3.1.2" or "tethering 3GS – 3.1.2" depending on the model of your device and install the package.
Step 3. Restart the iPhone and then browse to the site “www.unlockit.co.nz” with iPhone Safari browser to create a custom APN. Enjoy the tethering back to your phone.
Update : Our friend @Eagos created his own commcenter patch (actual patch) You can the complete instructions are also included on the page linked above. In Eagos words “ The one in cydia is basically replacing commcenter with the patched one which can be a problem depending on the state of your phone. So i wrote a program that ensures nothing of that will happen while its patching. Automated steps are taken in all in one package. The program do not use bspatch. It verifies commcenter version and validates it, then it patches it. It backs up the file first, unloads the commcenter 2nd, patch, loads commcenter and then reboots.”