How to Tether an AT&T iPhone 3GS or 3G running OS 3.1.2
WARNING: T3ch H3lp is not responsible if you mess up your phone, it would be your fault. We are not your mom.
*Erhm* lets begin. The entire process is pretty easy, and should take about 8-10 minutes. The proccess should work on both Windows and Mac OS X. We assume that you have not yet jailbroken your iPhone.
1. Download BlackRa1n for either Mac or PC here.
2. Plug in your iPhone
3. Run BlackRa1n
4. Hit the “Make it rain” button to jailbreak your iPhone. Your iPhone 3GS will almost immediately reset, and will soon display a picture of iPhone hacker Geohot. The entire process should take about 45-60 seconds. Do not interrupt this process by unplugging the cable or tinkering with your iPhone.
5. Once your iPhone has fully booted: Yippy! Your iPhone is now jailbroken.
6. Look for the Blackra1n icon on your iPhone’s homescreen. Open the Blackra1n app
Tap the label that reads “sn0w”, then hit the Install button in the upper right. This will unlock your phone for use on any SIM-compatible carrier, and reenable the IPCC hack required to enable tethering.. This part should take about 30 seconds.7. Once the unlock is complete, open Safari. Navigate to http://help.benm.at
8. Scroll down the page and tap “Mobileconfigs”
9. Find the proper IPCC file for your carrier. In the case of AT&T, that would be in U.S.A > AT&T. Tap this file, then hit the “Install” button. Confirm the resulting prompt, alerting you that the file has not been signed.
10. Allow the IPCC file to install, which will take about 10 seconds.
11. Close Safari. Hold the sleep and home button until your iPhone resets. This reboot may take a bit longer than normal.
12. When your iPhone resets, go into Settings > General > Network > Internet Tethering. If you can successfully switch the “Internet Tethering” slider to “On”: Congratulations! Everything seems to have worked as expected.