Occasionally, when I am done with a call on my iPhone 4, I try to hit the end call button and it's unresponsive. Basically, I can't hit the button. So the call will end when the other person hangs up, but then I can't hit ANY icon on the springboard. I have to restart my phone. Does anyone have this same issue? It happens maybe once every week or every two weeks. I was thinking about taking it to the apple store, but I don't know how to recreate the problem on demand.