I haven't seen anyone having this issue out of the numerous ones I've seen on this site. My iPhone 4's screen was sometimes going black. Hitting the home or power button wouldn't turn it back on. I'd have to hold down the home and power buttons to do a hard reboot to get it back up. I returned my phone yesterday to get replaced because I was also having the No SIM Card Installed error. My new iPhone 4 is having the same black screen issue occasionally, though.