There was a tricky way to tether but now it is much easier! You do not even need to use a pc/mac. You need to jailbreak your iPhone running on 3.1.2. Here are the steps!
1. Open Cydia on the iPhone.
2. Navigate to repositories (Sections > Repositories)
3. Find the repo. iPhone-notes.de
4. install and reboot then go to sources and find the iphone tethering package (it will be labeled either 3g tethering or 3gs tethering) install it.
5. go to this website on your iPhone http://www.iphone-notes.de/mobileconfig/
6. Install the US AT&T profile (it is close to the end. If there are two of the choose the first) no mailing address needed
7. Reboot the phone
8.You can find this in General > network > internet tethering
Disclaimer: AT&T could charge you a big bill for unauthorized tethering so use with caution.
1. Open Cydia on the iPhone.
2. Navigate to repositories (Sections > Repositories)
3. Find the repo. iPhone-notes.de
4. install and reboot then go to sources and find the iphone tethering package (it will be labeled either 3g tethering or 3gs tethering) install it.
5. go to this website on your iPhone http://www.iphone-notes.de/mobileconfig/
6. Install the US AT&T profile (it is close to the end. If there are two of the choose the first) no mailing address needed
7. Reboot the phone
8.You can find this in General > network > internet tethering
Disclaimer: AT&T could charge you a big bill for unauthorized tethering so use with caution.