What happens on the other end when you press "End call"
If you press "End Call" you effectively terminate the call and the other person is also immediately disconnected. 

If you don't want this to happen, you have to press the "hardware" volume down button to "silence" the phone or mute the phone with the hardware button (as far as I can remember). This way the phone will keep ringing but you won't hear it, and the other person won't notice it.