An homage to John Oliver's "Go FCC Yourself" campaign
This app uses the new RoleManager in Android Q to become the system CallScreeningService. This service type has been available since Android 7.0 (Nougat), but was only usable if the app was the current default dialer app.
When the service receives an incoming call, it rejects the call if the number is not in the user's contact list. The call will go straight to voicemail without ringing. It can optionally hide the missed call notification and not list the call in the dialer's call log