Hey, I successfully upgraded to 4.2.1 and jailbroke it using redsn0w 0.9.6b4. I was having some signal issues and wanted to see if the JB had anything to do with it, so I restored the iPhone 4 to stock 4.2.1 FW. Everything seems to be on the up and up, so I decided to re-JB it this morning. Just got done running redsn0w, and while Cydia shows up on my springboard, it will not open. It starts to, but automatically quits. I've re-booted the iPhone multiple times to no luck. I also tried re-running redsn0w to see if that'd work. No dice. Any ideas? I miss my custom MMS tones and MMS/SMS Quickreply apps! I'm on a Mac, BTW.