UPDATED 2-1-2010

I thought that I could update this thread with some new links and information. See the update ALL THE WAY AT THE BOTTOM.

UPDATED!

SEE BOTTOM OF THIS POST FOR INSTRUCTIONS ON HOW TO DO THIS FROM RIGHT ON YOUR iPHONE!

You can finally re-enable tethering on a iPhone 3G or 3GS running 3.1.2! It’s really simple, but, as with everything cool and awesome, you have to be jailbroken.

PATCHING COMMCENTER

Download THIS if you have a iPhone 3G and put CommCenter.patch on your desktop.

Download THIS if you have a iPhone 3GS and put CommCenter.patch on your desktop.

1. Transfer /System/Library/PrivateFrameworks/CoreTelephony.framework/Support/CommCenter to your desktop (KEEP A BACKUP OF THIS FILE IN CASE YOU WANT TO REVERT ANYTHING YOU’VE DONE!)

2. Open Terminal and cd to your desktop.

3. Copy and paste the following into Terminal:

bspatch CommCenter CommCenter-hacked CommCenter.patch

4. Delete the original CommCenter from your desktop.

5. Rename CommCenter-hacker to CommCenter.

6. Replace the old CommCenter from /S/L/PrivateFrameworks/CoreTelephony.framework/Support/

7. Change the permissions to +755 with your usual chmod tool (iFile can do this).

8. Reboot your iPhone, and see if Internet Tethering is there under Settings>General>Network. If not, go to step 9.

9. Go to http://help.benm.at from Safari on your iPhone.

10. Find a carrier profile for your carrier and install it, then reboot. If you’re on AT&T, use this.

You should now have Internet Tethering available in Settings>General>Network. Remember, if you get caught tethering from your carrier, we’re not responsible!

UPDATE! DOING THIS FROM YOUR PHONE

You can try downloading the proper CommCenter for your iPhone that is already modified, so that you can do all of this from right on your iPhone.

iPhone 3G (Courtesy of @besweeet) |   iPhone 3GS (Courtesy of @alnandr)

1. Download that file from Safari on your iPhone.

2. Use iFile to navigate to /var/mobile/Library/Downloads.

3. Extract the CommCenter file from the CommCenter.zip file.

4. Move this file to /System/Library/PrivateFrameworks/CoreTelephony.framework/Support, overwriting the existing file.

5. Make the permissions look like the below screenshot:

Follow steps 8-10 to finalize the process.

The only known problem with this so far is that the usage data will be incorrect when viewed under Settings>General>Usage. No big deal, though.

UPDATE, 2-1-2010

There have been a lot of updates over the past couple of months that makes tethering easier.

You can skip all of the CommCenter methods by either jailbreaking with blackra1n RC3, or redsn0w 0.9.2. If you used PwnageTool or blackra1n RC2/RC1, you still need to use the CommCenter patch above.

After you’ve used blackra1n RC3 or the latest version of redsn0w, just go to http://help.benm.at and find a carrier profile for your specific carrier. If you’re on AT&T, use this.