What happens, exactly, between someone tapping "call" and your Flutter app ringing on the other side? A lot — and most of it can fail. This talk traces one incoming call from push to pickup, built from a production deployment across a fleet of apps: the push that wakes a sleeping device, the native screen that shows over the lock screen, and the audio that connects over WebRTC. We'll dig into where iOS and Android part ways — PushKit vs. FCM, CallKit vs. Android's full-screen-intent and core-telecom split — and the background limits that kill calls on some phones but never your Pixel. You'll leave with a clear model of the stack and the traps to design around.