Again - putting words down that I have NOT said! I have repeatedly asked, "What troubleshooting steps have you taken?" to several posters only to hear nothing but silence. I guess I will have to write them out here.
The standard steps are outlined in the manual. These are all what Apple recommends and are also what the Geniuses will do if you go to the Genius Bar.
1. You start by powering the phone off, then turn it back on.
2. If the problem continues, you close out all the running apps, then perform a reset by holding down the home & power buttons until the screen goes black and you see the Apple logo.
3. If the problem continues, you back up and restore your software. Use iTunes for the best quality and most stable experience. Be sure it's the latest updated version.
4. If you're STILL having the problem, that could mean that there is some corruption in your backup file, or possibly one of your apps is causing the problem. In that case, you restore your device as NEW - you don't load your backup file. You use it that way for a few days to test it out. If the problem is solved, that proves it's something in your backup file or one of your apps. If it is STILL happening, it's a hardware problem and you should take your phone in to the Genius Bar (make an appointment first) to have it evaluated.