If it weren't for the fact that the exact, same thing started to happen a few days ago, when I still had my 3GS, I would be putting the blame on my new iPhone 4, which I just purchased yesterday. I upgraded to iOS 4 on my 3GS and all worked great for the first 10 days, or so. All of a sudden, I noticed that upon ending a phone call my screen would just be blank. The sensors do detect the phone is now away from me and the display illuminates but it's all black/blank. I'm able to end the call by touching the "End" button (it doesn't display, I just know where it's situated on the screen). I'm also able to lock the phone and unlock it by swiping even though there's nothing on the display other than an all-black screen that's lit. -- This happens on 50% of my calls. Additionally, on a few occasions my display has started to rapidly flicker (sort of like a strobe light) while I try to unlock my phone. It'll flick real fast for about 10 seconds and then it goes to blank/black (lit display, though). iOS 4 worked perfectly for about the first 10 days on my 3GS. Now i have my iPhone 4 and it's doing the SAME thing. Could it be that one of the recently updated apps in my library have some sort of bug that's causing this? Perhaps something in my media (music, videos, photos?) is the root of the problem? If so, any way I can try to discern what app or song is doing this? Is anyone else experiencing anything like this? Any help or suggestions are greatly appreciated!