Many of you asked for it and so here is the detailed guide on how to downgrade your iPhone 4, 3GS, 3G and iPod touch 2G / 3G running iOS 4.0.2 to iOS 4.0.1 / 4.0 / 3.1.3 / 3.1.2. The following step by step guide will help you rollback / downgrade to iOS 4.0.1 / iOS 4, iPhone 3.1.3 and 3.1.2 from iOS 4.0.2 as long as you have SHSH blobs saved for the respective firmwares for iPhone 4, iPhone 3GS, iPhone 3G and iPod touches.
iOS 4.1 Beta was seeded to developers yesterday. Since the iOS 4.1 is currently only jailbreakable on iPhone 3G and iPod touch 2G (non-MC model), you may want to downgrade your other iOS based devices from iOS 4.1 so that you can jailbreak them on iOS 4, or iOS 3.1.3 / 3.1.2 (formerly iPhone 3.1.3 or 3.1.2). The following step by step guide will help you rollback / downgrade to iOS 4, iPhone 3.1.3 and 3.1.2 from iOS 4.1 Beta as long as you have SHSH blobs saved for the respective firmwares for iPhone 4, iPhone 3GS, iPhone 3G and iPod touches.
Jay Freeman (Saurik), the developer behind the infamous Cydia store for iPhone has found a way to downgrade iPhone 3GS from firmware 3.1 to firmware 3.0. This process will only work for those who have saved their SHSH to Cydia Server, for more on SHSH, read the complete detail blog post by Saurik here. Also to note here is that while this method will help you downgrade your firmware from 3.1 to 3.0, your baseband will not be downgraded which means you cant unlock it for now.
The following step by step guide will help you downgrade your iPhone with firmware 3.1 to firmware 3.0.1. For those of you who upgraded to iPhone 3.1 may have found your device to be locked and un-jailbreakable as the tools for jailbreaking and unlocking are not out yet for iPhone OS 3.1. Fortunately, there is still a way to downgrade your phone from firmware 3.1 to 3.0.1. I have tried it on my iPhone 3G and it works perfectly on it.