AT&T unlimited tethering on iPhone 4, or jailbreak for iOS 4.0.2?

[Casey]

I have used an iPhone 3G (jb) as my primary internet access. It recently ceased to function, it has been "dieing" for a while, I had to replace the home button, then the battery and frankly its done more than I expect from Apple, granted however that isn't much. Now I have an iPhone 4, despite my adamant declaration I required iOS 4.0.1 or lower, for some BS reason about reported issues with 4.0.2, I got it and was not surprised to be set with iOS 4.0.2. I tried to no avail to exchange it for one of a lesser fw. Accepting I was stuck with that, I set to try and jb it regardless, after literally exhausting all possibilities I could find and come up with I have given up. So, if you have some way you think I probably haven't tried to jb it, by all means tell me. My primary concern now is maintaining my unlimited data plan I was grandfathered into, and for the time being, legally tethering it. Is there some means of doing so?