Apple had released iPhone firmware version 4.0.2 (IOS 4.0.2) to fix the iPhone security issue. This minor update however will not let you to jailbreak your iPhone using the web-based application (JailbreakMe 2.0 ‘Star’) through your iPhone safari, but iPhone 3G updated/restored to IOS 4.0.2 is still jailbreakable. I’m glad that I can show how you can jailbreak your iPhone 3G IOS 4.0.2 using redsn0w. Before you continue, please download redsn0w 0.9.5b5-5 and iPhone 3G IOS 4.0 here. Once you’re done, let’s get started.
1. Launch the redsn0w and click the browse button. Select open after you have located the IOS 4.0.
2. Once the iPhone firmware is identified, the next button will be active. Click it to continue. Now, you must check on “Install Cydia” and the rest of the selections are optional. Then, click next to continue.
3. Before you click the next button, make sure your iPhone 3G is connected to your computer and is switched off. If not, first connect it to the computer and then slide to switch off. When you’re done, click next to continue.
4. Now, you need to put your iPhone 3G into DFU mode. Just follow the redsn0w on-screen instruction, you can always try again if you fail for the first time.
5. Wait for your iPhone 3G to reboot after all files are uploaded successfully. You will see the Cydia on the home screen and your iPhone 3G is jailbroken successfully.
Well, I hope you will find this guide useful and enjoy the jailbreaking processes. As always, you can post any question about the jailbreak on the comment section.