Update: As of iPhoneOS 3.1, the iPhone will not accept unsigned config files (unless you have jailbroken); as such, this file will no longer work. If you have installed it (or any similar file for other carriers, like AT&T, T-Mobile, etc.) and upgraded to iPhoneOS 3.1 or 3.1.2, you will need to remove it. Open Settings > General > Profiles (at the bottom). Tap, then remove the profile you see there. Tethering should hopefully show up for you afterwards. I’ve preserved the rest of the entry for historical purposes, but it will no longer work on iPhone OS 3.1 or higher. More >