Haha… If you are too lazy to read through the entire iPhone iOS 4 user guide like me, you might don’t know this trick ~ take screenshot on iPhone 4.
How to take screenshot on iPhone 4?
Quickly press and release the On/Off Sleep/Wake and Home buttons at the same time. A flash of the screen lets you know the screenshot was taken. The screenshot is added to the Camera Roll album.
As simple as ABC.