It's official. Tethering is coming to the iPhone with the upcoming OS 4.0 update. Lets hope AT&T has upgraded their network enough to handle the extra data load. They wouldn't want a repeat of this little fiasco.
If AT&T messes this up, Verizon is set to pounce and swoop up a huge number of current AT&T iPhone subscribers. Simply put, Verizon's network is incredible and very stable comparatively.
More info here