So you just like voiding your warranty (it does, even if you lie about it and tell Apple you never did), and violating your contract with AT&T (and basically laughing at all of the people who pay the legitimate tethering fee by stealing it yourself instead)?
I'd say just get some free apps and be cool with it! Sounds like you're ok with everything else (even if you rationalize it)....
I have a 6GB data plan from Rogers and they don't charge me to Tether.
It's ridiculous to charge people to user data they already paid for.