TetherMe has been tested to work on all iOS versions from 3.0 to 4.0.1 and works by telling the iPhone to allow tethering on any APN that is used for iPhone data. As a result, you should not be charged extra from your phone company as all tethering data appears to come from the phone itself.
TetherMe also bypasses signature checking and allows you to edit your carrier bundle manually if you so desire. This is required to enable MMS functionality on T-Mobile. TetherMe does NOT enable the loading of APN configurations from .mobileconfig profiles at this time. This method should work on every carrier without any additional user interaction.
There is no icon for this item. After installation and reboot, tethering will be available to turn on in Settings -> General -> Network, or install the Tethering Toggle for SBSettings
You can search the app from Cydia and purchase it for $1.99.