How to use numberKeyListener to get keyPressEvents from the Android Dialler

Question

Can someone help me to get keypress events from the android dialler. can someone help me with it and should i use number key listener for it? I need my service to fire when the user presses 999 on the dialler.

Im just wondering wether i shud use a service for this or a broadcast reciever because i need the same input while the phone is locked or unlocked

Thank you Regards