The war over the legality of jailbreaking Apple devices was decided July 2010. The US Copyright Office ruled that jailbreaking your iPod was legal. Jailbreaking is altering your device to so it can download third party applications from vendors other than Apple. Jailbreaking your Touch depends on the firmware your device is using. Most Touch 4 users are using 4.1 firmware and use Greenpois0n to jailbreak their phone. Users operating with 4.0.1 firmware or earlier use the JailbreakMe website. Your firmware version is available in the “Settings” application under the “About” page of your Touch.
Click the link to download the “Greenpois0n” software to your computer. Click “Run” to download the software. Start the “Greenpois0n” software. Click “Run” if you receive a security warning.
Turn off your iPod Touch. Connect the Touch to your computer using the USB cord. Click the “Prepare to jailbreak” button.
Press and hold the “Sleep” button for two seconds. Press the “Home” button while holding the “Sleep” button. Do this for ten seconds. Release the “Sleep” button. Continue to hold the “Home” button for 15 seconds.
Click the “Jailbreak Now” button. The process of jailbreaking your iPod commences. Once the process is done, press the “Quit” button. The process should only take a few minutes.
Leave your iPod Touch alone to continue the jailbreak process. A large amount of script appears on your iPod screen. Once it is complete, your iPod reboots and powers back on.
Locate the “Loader” application icon. Select “Cydia” from the list. Click “Install Cydia.” Click “Remove” when prompted to uninstall “Loader.”
Once your iPhone completes the jailbreaking process, the Cydia app is available on your home screen. Cydia is the largest third-party application store available. From here, you can download new iPhone themes and apps to completely customize the appearance and functionality of your iPhone 4.