Been keeping a close eye on the monthly bill and still no charges. Using the benm tethering & MMS hack. Only change to the bill has been the MMS messages show up on the bill with $0.00 charges.....
This would be a question IF ATT ACTUALLY offered a tethering service, seeing as how they don't, what would they say even if they found out? Like they can't charge you for getting a non-existent service for free?!
To be on the safe side keep your monthly data usage at a reasonable level 5GB is fine, but 15GB may look suspicious, lol.