Tell Tii - Unauthorized Tethering

Hey Rob,  Longtime Listener, First time E-mailer, just to share some more info on unauthorized tethering

I have a iPhone using T-Mobile USA,
Recently, I started getting Texts from T-Mobile too, saying they they would block my Tethering, if I continued, I ignored them.
I am using a grandfathered in Edge 5.99 Data plan.

Then I got a Text Message saying they did block it.
I tried to Tether again, it sends me to a T-Mobile Website asking me to change the Data plan to a more expensive one with Tethering.
This was on both MyWi, & TetherMe.

However, iTunes continue to work normally, so to is Skype, you know items that doesn't use a regular internet browser.
Then I tried to PdaNet, and boom no problems. so PdaNet does something different with the Hide Data Feature.

so this presents 2 points, couldn't ATT just block tethering in a way such as T-Mobile, instead of force Upgrading?.
and this pretty much confirms that ATT is may not just be guessing who is tethering by looking at data usage.

Thanks,  

 Anthony C