Jailbreak iPhone 3g 4.2.1 Redsn0w

These are instructions on how to jailbreak your iPhone 3G on the 4.2.1 firmware using RedSn0w for Windows.


Step One
Create a folder on your desktop called Pwnage

Download RedSn0w from here and place it in the Pwnage folder. Likewise, download the latest 4.2.1 firmware from below and place it in the same folder.

4.2.1 (3G): iPhone1,2_4.2.1_8C148_Restore.ipsw

Extract the redsn0w executable from the RedSn0w zip file into the same folder.


Step Two
Connect your iPhone to the computer and launch iTunes.


Select your iPhone from the list of devices on the left. Now hold down Shift and click the Restore button. Restore is preferred as it won't create any wasted space on your iPhone.


Navigate to the Pwnage folder on your desktop and select the 4.2.1 firmware ipsw. Click the Choose button to continue.


Step Three
Once iTunes has finished updating your iPhone to the desired firmware open the Pwnage folder on your desktop and launch the redsn0w application from the redsn0w folder we extracted earlier.


Step Four
Once RedSn0w opens click the Browse button


Step Five
Select the 4.2.1 firmware ipsw we placed in the Pwnage folder on our desktop then click Open.


Step Six
Once the firmware has been verified click the Next button to continue.


Step Seven
RedSn0w will now prepare the jailbreak data


Step Eight
From this window you can select the jailbreak options you would like.



Make sure Cydia is selected. And you can Enable multitasking, Enable homescreen wallpaper, and Enable battery percentage. If you do not need multitasking we would recommend deselecting it as it makes your iPhone 3G run very slow.

And check Install iPad Baseband , Click Yes when prompted to confirm your decision.


Click the Next button to continue


Step Nine
Please plug your iPhone into the computer and make sure its OFF then click the Next button


Step Ten
RedSn0w will now guide you through the steps to get into DFU mode. You can find more help with DFU mode here


Hold down both the Home button and the Power button for 10 seconds.


Release the Power button and continue holding the Home button until RedSn0w detects the device.


Step Eleven
RedSn0w will now downloaded the iPad baseband if needed and your iPhone will reboot


Step Twelve
RedSn0w will then begin uploading the new RAM Disk and Kernel.


Step Thirteen
Once this is complete you will be notified that RedSn0w is done. Click the Finish button. When your iPhone finishes rebooting (5 minutes or so) it will be jailbroken with Cydia on the SpringBoard.


Then you can unlock your iphone with ultrasn0w, tutorial
 
NOTES:
If you have problems with RedSn0w on Windows Vista or Windows 7. Right click the executable and set it to run as administrator in Windows XP compatibility mode.

Source : iclarified.com