Firstain

Remember this is a hack so please do not blame us if Apple does anything to your device.

Guide:

1. To commence, download and install iTunes 9.2 (Mac only, download links here, here, or here).

2. Now you need to download the right gold master for your device and save it on your desktop:

• If you have an iPhone 3GS, download this.
• If you have an iPhone 3G, this one is for you.
• iPod Touch 3G, get yours here.
• And finally if you have the iPod Touch 2G, download this.

3. Now let’s actually install iOS4:

• Plug in your iOS device, and then tab over to iTunes.
• In iTunes, alt+click on the ‘restore’ button, and then when promoted to locate the file select the IPSW file we just moved to your desktop.
• Wait for between 10 and 15 minutes for the new OS to be moved over.
  

  iOS 4

  Credits:thenextweb

Related posts:

1. iOS4 Unleashed: Download yours now! (UPDATE: Not Yet!)
2. With new iPhone comes new iTunes: Version 9.2 released with iOS4 Support
3. Speeding up iPhone 3G and iPod Touch 2G using iOS 4 (video)
4. Android 2.2 now on your Apple iPhone
5. How to reset your Apple iPod or Apple iPhone Password from your PC?