Implementation of loudspeaker, hold, mute, conference like basic functionalities #12

I like your efforts, and would like if you take it to next level.
I try to develop calling screen with basic functionalities like loudspeaker, hold, mute, conference, etc.
It's possible to access these privileges by making our own default dialer.
I successfully implemented this but can't able to implement these basic functionalities.
Can someone help me?
Thanks.