I am on a locked AT&T iPhone. I do not want to jailbreak and am trying to enable Internet Tethering. I have not had any success with the ipcc files and I am willing to work with anyone to try to figure out how Apple changed the APN's for AT&T.
I am under the impression Tethering is a separate APN because if you look at this URL iPhone: About Cellular Data Network settings (viewing or editing the APN) Apple shows a separate APN category for tethering and at the bottom, say basically it's only available with 3.1.3 on an authorized, unlocked carrier.
I also have successfully upgraded and downgraded between 3.1.x to 3.0.x WITHOUT deleting any settings. Nearly everything remains intact and if I can get some help I am more than willing to make a tutorial to this effect.