How To Jailbreak Ios 4.2 1 Iphone 3g

jailbreak ios 421 with redsn0w Redsn0w 0.9.6b4 works to jailbreak iOS 4.2.1, but for many devices it remains a tethered jailbreak. A tethered jailbreak means that you have to connect the iPhone or iPod touch to your computer and run redsn0w every time the device reboots or runs out of battery. Only the iPhone 3G, older iPhone 3GS, and older iPod touch 2G will work untethered with redsn0w. I would recommend most users wait for an untethered jailbreak since it will be easier in the longrun, but if you're determined to jailbreak the latest iOS, here's how:

How to Jailbreak iOS 4.2.1 using Redsn0w 0.9.6b4

The instructions are the same for Mac or Windows. This guide requires you to have iOS 4.2.1 and iTunes 10.1 installed before you begin.

If you haven't already, download redsn0w 0.9.6b4 for Mac or Windows
Download the IPSW that you need for your device from the iOS 4.2.1 direct download links
Once the IPSW file and redsn0w have downloaded, open the Redsn0w 0.9.6b4 application and click "Browse"
Select the IPSW file you just downloaded

jailbreak ios 421 with redsn0w

Select that you want to install Cydia
At this point you follow the instructions on screen: Make sure your device is turned off and plugged into your computer, then click "Next"
Again, following the instructions on screen you need to put your iPhone into DFU mode by holding the Home and Power buttons together for 10 seconds, then release the power button but hold onto the Home button for another 3 seconds.
You might see some gibberish appear on your iPhone screen, this is normal.
Click "Finish" and your device will be jailbroken

Extra step for iPhone 3GS, iPhone 4, and newer iPod touch with redsn0w jailbreak:
If you encounter problems with Cydia running on any of the tethered devices, you need to reboot the hardware and reconnect it to redsn0w with the "Just boot tethered" option enabled. After you do a tethered boot, Cydia will function as usual.

tethered boot redsn0w ios421

How to boot tethered jailbreak with redsn0w 0.9.6b4

If you have a device that requires a tethered jailbreak, anytime you reboot your device you will need to do the following:

Connect your iPhone or iPod touch back to the computer
Launch redsn0w 0.9.6b4
Select "Just boot tethered right now" and then click "Next"

Your tethered jailbroken device will now boot as usual. Due to the hassle of tethered booting, I do not recommend most users jailbreak iOS 4.2.1 using redsn0w, instead you should wait for a new version of PwnageTool or limera1n/greenpois0n, both of which are due shortly and they will be untethered jailbreaks.

Redsn0w is not an unlock! Remember, if you have any intention on ever unlocking your iPhone, do not use redsn0w and do not upgrade to iOS 4.2.1 yet. Instead, save your SSH blobs from iOS 4.1 and wait for further unlock instructions.