I. Before You Begin
1. This is only for the iPhone 3G on iOS 4 (aka iPhone OS 4). NOT iPhone 4 or iPhone 3GS!
2. This will work on all basebands up to 5.13.04 (check your baseband by going to Settings > General > About and looking for Modem Firmware).
3. In order to unlock the iPhone, you must do this procedure and then go to our next procedure called How To Unlock the iPhone on iOS 4 linked at the bottom of this procedure.
II. Download all the necessary files
1. Download iTunes 9.2 if you don’t already have it:
2. Download RedSn0w (the jailbreaking program we’ll use)
3. Download the iPhone iOS 4 firmware file
III. Jailbreak the iPhone
1. Install iTunes by double clicking the iTunes Setup file you downloaded just now.
2. Plug the iPhone in via USB cable and let it pop up in iTunes and sync it with iTunes.
3. Now, update your iPhone 3G to iOS 4 through iTunes if you haven’t already.
4. Once it is on iOS4, unzip the RedSn0w .zip file we downloaded.
5. Inside the extracted folder, right click on RedSn0w the application, and click Run As Administrator (if using XP, or Mac you can skip running as admin and just double click it).
6. In RedSn0w click Browse and search for the iOS 4 Restore file you downloaded and select it.
7. Once it says successful, click next. On this screen check off what you want to enable (the default options are fine) and then click next.
8. Turn off your iPhone and leave it plugged in.
9. Click next in RedSn0w and it will tell you to hold certain buttons on the iPhone to get it into DFU mode. Once it is in the correct mode, RedSn0w will automatically start running. Wait for it to finish.
10. Once the phone reboots, you have a jailbroken iPhone 3G and should see Cydia listed in the apps list on the homepage.
11 (Optional). TO UNLOCK THE PHONE, continue to our next procedure: How To Unlock the iPhone 3G/3GS/4 on iOS 4