Problem: Screen Shuts Off For No Reason

Question

I have the new iPhone 3G.
My screen shuts off (the screen turns black, but the phone is still on...like if you shut the monitor off on a desktop PC while the tower is still on) randomly which requires me to do a hard reset (holding the sleep button at the top of the phone and the home button at the same time until the Apple logo appears).
This happens without warning when I do the following:
1. During a call, when I need to use the keypad, put a call on hold, activate speakerphone, etc. the screen will stay black and will not turn on when I touch it. This means I can't even end a call unless the caller hangs up. It is clear that the phone is still on (I can hear the caller at the other end), but I cannot use the screen at all. The screen comes back on when I put the phone back up to my ear, but then when I pull it away to touch the screen it goes black again.
2. After I complete a call, the screen will shut off before I can press the "end call" button. Even after the call is terminated from the other end, I cannot make the screen come back on.
3. After the screen automatically goes to sleep (goes black), I cannot make it come back on.
In all 3 of these instances, I use a hard reset to make the screen come back on. In the first instance that I listed, I have to do a hard reset during the call in order to disconnect the call and get the screen to come back on.
These problems do not happen during/after every single call. For example, sometimes it will be after one call, other times it will be after five calls. It happens without warning and without reason. It is very inconvenient because I am resetting my phone several times a day. When I call customer service lines (for any company), I can't use the keypad to do things such as "Press 1 for English" without doing a hard reset in the middle of the call and calling back several times until it works.
I would really appreciate it if you could offer some advice on how to fix this problem.
Thank you.

Answer 1

I had the same problem, and a very helpful person in another thread suggested I try removing the phone from the case, as it's probably blocking the little sensor next to the earpiece. When it's close to your head, the display shuts off (because, naturally, you're not using the screen). When you take it away, the screen should pop up. If that sensor is blocked, the thing thinks it's still next to your head.
I'm going to experiment without the case for a few days. if it's fixed, great. If it's not, I'm taking the stupid thing back to the Apple Store. We'll see.
Course, if you don't have a case... I'd say either attempt to erase and restore it from within iTunes or get on the horn with Apple support.