Most of it is in post #5 above; not that it matters, because it doesn't actually make tethering work.
Originally Posted by wonderroom
You edit the file /var/mobile/Library/Preferences/com.apple.MobileInternetSharing.plist with a plist editor (see my signature) to change the value of the key State from 1020 to 1023.
Also, in /var/mobile/Library/Preferences/com.apple.carrier.plist there is a section with the connection parameters of your EDGE/GPRS connection, at the apns key. In between the apn, password and username, you add another key:
<key>type-mask</key>Or you can do this by installing a "provisioning profile" that takes care of the carrier settings: navigate Safari on your iphone to this menu and install the profile of your carrier.