A method of “hacking” the 3G/3GS for tethering has been found but you need to be jail broken 1st.
Instructions are HERE and I accept no responsibility if it breaks your iPhone (you may have to reinstall again if you break it).
Also I have copied the instructions here:
- First get this file and put CommCenter.patch on your Desktop:
- Copy /System/Library/PrivateFrameworks/CoreTelephony.framework/Support/CommCenter to your Desktop also.
Open the Terminal and:
- bspatch CommCenter CommCenter-hacked CommCenter.patch
- Now go ahead and delete CommCenter now from your Desktop and rename CommCenter-hacked to just CommCenter.
- Rename CommCenter on your iPhone to CommCenter.backup in case something bad happens, so you have a backup.
- Copy the new CommCenter to your iPhone.
- SSH into your iPhone or use MobileTerminal as root and chmod +755 the new CommCenter so that it’s executable.
- Restart your phone.
It simply removes the test for testing for the tethering signature thus enabling tethering on your iPhone 3G/3GS on 3.1.2 firmware.
After you have done this go to http://www.unlockit.co.nz on your iPhone and download the config for your carrier.