You iphone AT&T customers are still prohibited from tethering your phone, using it as a modem. That was one of several reasons (non-removable battery, AT&T service being two more) that I am a happy G1 owner, as opposed to an iphone owner.
When my broadband goes down at home, I use my G1 to tether to T-Mobile 3G, and I am back up on the internet within a minute.
It supports tethering.
I tether my iphone to my laptop all the time, works like a champ.