I want to block calls from few numbers, for that I want to write a app of my own. So what are the APIs which I should be using?
Basically I want to get notified when a call comes, i want to compare numbers if it is what i want to block, i want to cut the call or mute it or if possible mute it and record it.
You could just re-direct specific numbers in your contacts to your voice-mail. That's already supported.
Otherwise I guess the documentation for 'Contacts' would be a good place to start looking.
You can do it by listening to phone call events . You do it by having a BroadcastReceiver to PHONE_STATE and to NEW_OUTGOING_CALL. You find there what is the phone number.
Then when you decide to end the call, this is a bit tricky, because only from Android P it's guaranteed to work. Check here.
