I just got my Verizon iPhone 4 last night and jailbroke it, I might rethink the free tethering now though because Verizon will probably follow.
http://www.bgr.com/2011/03/18/att-cracks-down-on-tethering-cheaters/
http://www.bgr.com/2011/03/18/att-cracks-down-on-tethering-cheaters/