Hello. I've tried to read up on this issue so much that I'm dizzy. I'm hoping someone has the patience to help. I have an iPhone 3G that had a service contract with AT&T in the U.S. When I moved to China, I jailbroke/unlocked the phone myself and got a sim card and service from China Unicom. But over the last nine months, the iPhone's functionality has degraded: apps quit unexpectedly, Cydia doesn't work anymore (quits on launch), iTunes plays erratically, SMS doesn't present, phone reboots at will, etc. So instead of a first-time jailbreak/unlock, I need my iPhone to be RE-jailbroken/unlocked. I'm at OS 4.0.2, which I've read may be part of the problem. What are the gotchas of doing a clean jailbreak/unlock of my iPhone in its current bad state and that will allow me to continue using my China Unicom sim card? For example, can I simply reset my iPhone via iTunes and start over using the instructions posted here? And should I remove my sim card when I do all of the procedures, or can I leave it inserted? Thank you (profusely!) in advance for your help.