When the iPhone 3G 3.0 update came out, we were expecting some kind of tethering for people like me that goes on the road a lot and need the laptop connected to the web in regular basis. AT&T didn’t supply that option and they might be adding that for a huge monthly fee.
Now some people found the way around that problem and how to do it, in 5 minutes following this instructors your laptop can be online connected to your iPhone via USB or Bluetooth.
All the details to do that takes 5 minutes and can be found here at iSmashPhone
http://www.ismashphone.com/2009/06/activate-internet-tethering-now-on-iphone-os-30.html
Follow those instructions to be able to activate your iPhone for tethering. Now this is not what AT&T wants you to do, so they may charge you if they find out and of course that application to unlock the feature is not being tested by Apple.
Cheers
Al