Update AT&T iPhone 4 to iOS 4.2.1 and maintain unlock
The AT&T iPhone 4 I purchased back on launch day is still running, despite being dropped into a puddle of water some time ago. I’ve gotten a lot of use out of it, and it’s truly a terrific phone.
Today I finally updated the phone from iOS 4.0 to iOS 4.2.1. Since I’m living in Vietnam, it’s a requirement that the phone be unlocked, and I wanted to wait until I was 100% sure I could update the phone successfully.
The other reason is that I had chosen the “Reset All Content and Settings” option in the Settings app, before learning that this process can take many hours– and still fail to work. Doing a restore using PwnageTool 4.2 was quite straightforward, provided I have the right .bundle and .ipsw files.
After restoring the phone, I needed to run Cydia and re-install ultrasn0w. That did the trick; the phone is now working perfectly, running iOS 4.2.1, and having none of my old data on it :)