When your mobile rings and your CLI (Call Line Identification) shows somebody whom you do not with to speak to, simply press the CLR key and the ringing will stop on your end. Take note that the phone is still waiting for you to press Yes (to answer the call) or No (to send the busy signal). This way, the caller will continue to hear the ringing signal on their end while you have the option to mute that ring and let the call divert to your voice mail, etc.