I think their system is flawed. I hadn't used EasyTether in a LONG time when I got the email from them about tethering this week. I went to a store and had them inspect the phone to ensure that I don't have any way to tether so they added it in my notes.
Next day I got a txt saying that I am still tethering so I called the number in the txt and told the woman that I am not able to tether even if I want to and that the store verified that in my notes (which she did see). She claimed that ANY connection to a computer now (i.e. charging and file transferring) can be detected by the system and misconstrued as tethering, and I did charge off the computer the night before getting that txt so to me it almost seemed possible that their systems could be inaccurate like that. But then she said when I use bluetooth to stream audio from my phone to my car that is also counted as tethering and I don't buy that at all.
I asked her if they're just threatening me because I always use a ton of data and she said no because I am unlimited and I can use whatever I want as long as I am not connected to anything else.
And now yesterday I got snail-mail from them about tethering. Which I have not been doing. In any way whatsoever.
Makes me wonder if they have access to my Market transactions and see that I once downloaded EasyTether last year. So frustrating.