I ALWAYS close my apps as soon as I'm done using them, except for Messages (I'm basically constantly texting, so it always stays open). However, whenever I close Messages (the only app open), my iPhone 4 locks up. It's stuck on the graphic of the multitasking dock open (as if I had double tapped the Home button), but nothing is open in there. Hitting the Home button, tapping the screen, even hitting the Sleep/Wake button do nothing. The only thing I can do is wait for approximately a minute for it to come back to life, or force a reboot by holding the Sleep/Wake button down for a few seconds. Can anyone else test this out and see if it happens to them as well?