I have an iPhone 3GS on 4.2.1 with a baseband of 05.15.04. As I understand it, if my baseband is upgraded to 06.15, I won't be able to re-load my factory defaults, or cover up my jailbreak if I need an exchange. I don't care about unlocking, I'm using the phone on AT&T anyway. So is there a way to jailbreak 4.2.1 on my 3GS while leaving the baseband as it is, meaning that I could still factory reset, etc, if needed? Most of the guides I've found either say they DO upgrade the baseband, or are vague as to whether or not they do.