Had 3 iPhone 4s replaced in 2months, I don't think it is Apple's quality. I've been using iPhones for a long time now and only 2 months ago. My iPhone 4s kept on shutting down (log shows panic.plist) Lucky it was under warranty. No water damaged. No impact damage. Apple store decided to replace it. The first replacement: Within an hour, it too shuts down, can't be woken from sleep and I have to force restart (power + home buttons) to get it turning on. It would do this 10-12 times a day. No Apps were installed and I tried factory resetting as well. I took it back to the Apple store and they replaced it The Second replacement: Exactly the same thing. I now have this 2nd replacement in front of me, living with the "force reset", I have been doing this for 3-4 times a day for the last month. I don't think it's Apple's quality control. The only thing (a bit of a stretch) that I am suspicious of is the SIM card? That is the only piece of hardware that has followed me throughout the three iPhones. Is there a possibility it is a corrupt SIM? I can still call and text normally though. I'll try giving support a call but thought I'd see if any forum users have suggestions, ideas or personal experience with this problem.