InCallUI must handle a hardware nightmare: the proximity sensor. A bug here causes "black screen of death" (can’t hang up) or "pocket dialing" (screen on during call).
Because InCallUI is a system app with high privileges, bugs within it can severely impact device usability.
Displaying the buttons for mute, keypad, speaker, hold, and adding calls.
Historically, InCallUI was monolithic. Today, it operates as a collection of interacting services:
Its core responsibilities are: