I have an iPhone 4 (MC605C) on iOS 4.0.1 and baseband 01.59.00. It is currently jailbroken using jailbreakme.com and unlocked with Ultrasn0w. According to Cydia, I have SHSH blobs for iOS 4.0.2, 4.1, 4.2.1, and 4.2b3. I would like to update to iOS 4.2.1 (and then jailbreak with greenpois0n) while preserving my baseband.
My question is, do I need to undo the jailbreak before upgrading to 4.2.1? Or can I simply follow the steps outlined here?
If I do need to undo the jailbreak first before updating, how exactly do I do it?
Thanks a lot for your help.