I did search on a number of forums on this and I'm still confused. After resisting from JB for a long time I finally did it using QuickPWN on my 3G 2.1 firmware. I did it because after researching I was led to believe it is completely undoable. Now it is not so obvious. I played with jailbroken phone, installed some apps, unistalled and finally decided to go back to the original (due to some performance problems). I restored the original 2.1 firmware and everything went OK. Due to some (apparent) network problems (not being able to receive calls on 3G) I was planning to send the phone to the repair. Again did some research on removing all the JB traces. It occurs that the restore process does not completely cleans the iPhone as there may be some files left by the applications like Winterboard, Cydia, or Installer. I found a couple of methods and still not sure which is the proper one. 1. Just restore the original FW 2. Restore and erase all content and settings and register as new device in iTunes 3. Restore in DFU mode ...and so on. Using the QuickPWN there is also a note that the baseband has been updated to the "correct one". Can someone kindly explain how to remove all the traces of jailbreaking on a phone that's not bricked and working fine? I want to do that while "I can" and it's working in case I need to send it for repair in the future. All I did was restore in DFU and also I'll erase all content and settings tonight. However I don't understand why to register as new device and not to use previous backups. As I mentioned, I did search for a clear solution but I'm still confused.