iphone has been working perfectly until yesterday when I received a phone call, and the screen was completely black. Home button didn't work, couldn't power off...but the phone still kept ringing until it went to voicemail. Finally got a text 20 minutes later, then the phone was working properly. Has anyone experienced this. I was 2 minutes from getting in my car to go to the Apple store to complain...politely of course...and then it came back on. Any suggestions or help would be greatly appreciated.