LG GD550 User Manual page 69

Profile switch
Turns the sound on or off from any screen including the lock
screen by sliding it up and down. (Incoming call, listening to
music, alarm rings, and etc.)
This is only for the sound. If you want to change the settings for
vibration, go to More > Settings > Tones > Call and message.
Vibrating alert is set to On as default.
Headset / Charger /
USB Cable connector
Volume key
Controls the volume
of the earpiece.
Camera key
Goes to camera menu
directly from the
homescreen.