Step-by-step Tutorial: How to Tether Jailbreak iPhone 4 Using RedSn0w 0.9.10 (Windows) [iOS 5.1]
UPDATE: Apple released iOS 5.1.1 and has stopped signing iOS 5.1, so you can NOT restore to 5.1 any more (both original and custom), unless you have saved your SHSH keys for 5.0.1. If you are on 5.1 you can jailbreak with redsn0w. iOS is also tethered jailbreakable with redsn0w.
This is step-by-step instructions on how to perform tethered jailbreak of youriPhone 4 on iOS 5.1 firmware using RedSn0w 0.9.10 for Windows.
Tethered jailbreak means that each time you restart your device you will need to connect it to a computer and run redsn0w.
Important: Please, consider reading our Jailbreak & Unlock FAQ, if you have other device or firmware and especially if you have questions or troubles.
Please think first, before you do something.
If you have iOS 5.0.1 firmware - you can do an untethered jailbreak using one of our tutorials.If you need carrier unlock - do not update to iOS 5 firmware, use RedSn0w or Sn0wBreeze to create a custom firmware to preserve modem version!
Create a folder on your desktop (or any other folder on your computer) called Pwnage
Download the latest version RedSn0w 0.9.10 from here. Save it in the Pwnage folder.
Extract the redsn0w executable from the RedSn0w zip file into the same folder.
Connect your iPhone 4 to the computer and launch iTunes.
Select your iPhone from the list of devices on the left. Create a backup by right-clicking on iPhone name in Devices (iTunes left pane) and choosing Back Up.
If you are already on iOS 5.1 you can now skip to step three.
Download iPhone 4 firmware iOS 5.1 to Pwnage folder. It is better to use Firefox, because some browsers (f.e., Safari) extract ipsw: