Earlier today we told you that iPod 4 jailbreak and iOS 4.1 jailbreak development is in progress. According to iPhone hackers chronic dev team (posixninja, pod2g) manage to achieve iOS 4.1 jailbreak exploit. But no one talked about baseband exploit to unlock latest baseband. So we strictly advise you to stick with iOS 4.0.1 if you care for your unlock. 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 4.1 Notcom released the latest version of Firmware Umbrella with this useful feature. You can download the latest version of firmware umbrella from official site http://thefirmwareumbrella.blogspot.com/
You need to have your iOS 4.0.1 SHSH saved on Cydia or locally.
This will only work while Apple is signing 4.0.2 SHSH requests.
You can downgrade to iOS 4.0.1 anytime, only if you satisfy first point mentioned above.
Step One : Close iTunes, Skype, Messengers or any other background application.
Step Two : Launch Tiny Umbrella and connect your iPhone 4
Step Four : Now launch iTunes and restore to iOS 4.1 (download here) Note : do a *Restore* not *Update*
Step Five : Cross your fingers and wait for iTunes to end up with error 1004. This is perfectly normal and has to do with the baseband not being updated.
Step Six : Simply ‘Kick Device Out of Recovery’