Really, you haven't heard?
In a nutshell, Verizon bought Alltel and the FCC said in the markets where Verizon and Alltel were the dominant carriers, Verizon has to divest those markets... sell them off.
Here is your proof of AT&T looking at us Alltel customers:
http://news.cnet.com/8301-1035_3-10156765-94.html
So.. now back to my question, how does AT&T know when you tether a phone such as a PPC-6800/Mogul using Windows ICS?