How to open camera app when the iPhone is locked?

This is a new feature comes with the iOS5. You can open the Camera app right from the Lock screen. Use grid lines, pinch-to-zoom gestures, and single-tap focus and exposure locks to compose a picture on the fly. Then press the volume-up button to snap your photo in the nick of time. If you have Photo Stream enabled in iCloud, your photos automatically download to all your other devices. So how to open camera app [...]