The phone contain alot of Hardware which includes: ear piece(for hearing your caller) when faulty your caller may hear you but you can't hear him/her.
Mouth piece(it act as a micro phone that transmit your speech to the reciever(your caller) when faulty your caller may not hear you.
Ringer(server as the outside speaker,playing music) when faulty your phone doesn't ring or play music outside.
LCD Screen(use to display the phone activities) when faulty or broken, there is no display.
Keypad(for typing).
Antena(for recieving network) when faulty the phone might experience network failure.
Vibrator(it causes the phone to Vibrate).
Camera(for taking photographs)