UNBELIEVABLE! YOU'VE GOT TO READ THIS. I SWEAR TO ALL MIGHTY, IT'S TRUE.
This is for all you people out there with iPhones that the slider lock occationally becomes unresponsive upon an incoming call, you can be assured that this is normal. I got this directly from Jason, a Senior Advisor at Apple. Don't waste your time trying to figure out why it's happening, just accept it. Oh, by the way, this is a great excuse to not answer the phone when the boss calls! Just tell him that it's normal for the iPhone to not act like a phone every once in a while.
Here's the whole story: Since I got my iPhone in June 2011, I've been having the problem of the lock slider not responding upon an incoming call every so often. Since getting the iPhone in mid June, 2011, I've been to AT&T, been to the iStore for reboots and restores, replaced the SIM card, and exchanged the phone for a new one five (5) times. On August 17th I contacted Apple Support and spoke with Visrat who later transferred me to Jason, a Senior Advisor. Jason had me do a restore even though I explained that the phone had already been replaced a number of times and I had also done some restores in the past with the problem only coming back. I went through the process and the phone worked okay for 15 days where upon it locked up twice in two days. After this, Jason and I played phone tag for a few days until today (September 12) we actually spoke. Jason explained that since I was still having the problem that this is normal for the iPhone. I told him that this was not acceptable and that it does not make sense that so many people are having this problem. I told him that my company has many employees using the iPhone and that nobody that I speak with at my company has the problems that I've had. Jason explained that there was nothing more he cold do for me.