Earlier today we posted a guide to Jailbreak iPhone 4, iPhone 3GS iOS 4.2.1 with Greenpois0n RC5. As you know Greenpois0n requires your iDevice on stock iOS 4.2.1 and those who rely on ultrasn0w unlock must stay away from Greenpois0n jailbreak.
Fortunately Notcom, guy behind firmware umbrella discovered a method to preserve your iOS 4.0.1 / 4.0.2 baseband 1.59.00 while updating to iOS 4.2.1 (iPhone 4 only). Notcom released the latest version of Firmware Umbrella with this useful feature. Following are the instructions so you can update your iPhone 4 to iOS 4.2.1 and use greenpois0n without loosing the ability to unlock. You can download the latest version of firmware umbrella from official site http://thefirmwareumbrella.blogspot.com/
Step One : Close iTunes, Skype, Messengers or any other background application.
Step Two : Launch Tiny Umbrella and connect your iPhone 4
Step Three : Hit the Start TSS Server button.
Step Four : Now launch iTunes and restore to iOS 4.2.1 (download here)
Note : do a *Restore* not an *Update*
Step Five : Cross your fingers and wait for iTunes to end up with error 1013. This is perfectly normal and has to do with the baseband not being updated.
Step Six : Simply ‘Kick Device Out of Recovery and that’s it. Now you can follow our guide to Jailbreak iPhone 4, iOS 4.2.1 with Greenpois0n RC5
Note : if Tiny Umbrella Fails to kick your device out of recovery mode than ran greenpois0n and that’s it.
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