Previously I have elaborated about How To Jailbreak iPhone 3GS OS Firmware 3.1.2 With PwnageTool For Mac but something bad happens because afterward you will be losing your internet tethering ability since Apple doesn’t support internet tethering in firmware 3.1.2.

But worry not because you still can get the tethering back for your iPhone 2G, 3G, and 3GS albeit OS 3.1.2 firmware installed using an application named MyWi.

How To Enable Internet Tethering on iPhone 3G and 3GS with OS 3.1.2 Firmware:

• On your iPhone, open Cydia and look for MyWi and then install the application and at the same time RockApp will also be installed.
• Begin RockApp and create a free Rock ID , to do so head to Manage -> Rock ID and create the new RockID
• You’ll be prompted to update the MyWi app, do so, after it’s updated then restart your iPhone.
• Open up MyWi app and turn the option for USB/Bluetooth tethering to on.
  5. Navigate to Settings > General > Network > Internet Tethering and toggle the Tethering ON

Conguratulation now internet tethering is available on your iPhone OS 3.1.2 now