To grab or take a screen shot or capture in iPhone is by use the
home and
power/lock keys. It affects to iPhone that uses iOS 2.0 or higher. Whatever your iPhone device, 3G, 3GS, 4, 4S or 5, you can use this trick without additional application.
How to capture :
Open the screen you want to take a screenshot
Press and hold the
Home button
During you hold the home button,
press and
then
release the
Power/lock button to start capturing.