Verizon and AT&T are both cracking down on data usage, both with capped data plans and now stopping illegal tethering. iPhone users longing to tether always had the choice of jail breaking their iPhone and using apps such as MyWi to tether to another WiFi device.
AT&T was the first to make this move with some harsh consequences for tethering. Any iPhone user who is using a illegal tethering app will be put on a tethering data plan automatically.
Verizon was a bit less harsh, giving users a chance to choose. If you try to tether using one of these apps, you will be forwarded to a webpage that offers you an upgrade to tethering data plans.