Like on Notebooks or PC, Sometimes an application iPhone programs can sometimes crash and lock up your iPhone system. These crashes are rare on iPhones, but when they do show up, it’s important to know how to force quit iPhone programs. While the application is open(the one that is causing the problem), press and hold the home button. Just hold down the home button at the bottom center of the iPhone for about 8 seconds. This will quit the program app or game and return you to the main home screen.
There are actually two different ways to do this, depending upon the version of the iPhone or iPod Touch OS that you are running.If you really need a way to tell, try swiping your home screen (the one with all of the icons) all the way to the left. If you find the Spotlight search page to the left of your first page of icons, then you want option number one here.
then you want option number two:
1. For devices running 3.0 or later – Press and hold the sleep/wake button until the slide to power off screen appears. then press and hold the home button until the application quits (5~8 Secs)
2. For devices running software before 3.0 – Just press and hold the home button for about 8 seconds, or until the see the currently running application close. Voila, no more frozen app.