Callkit

This covers the full lifecycle of building VoIP calls that integrate with the native iOS call UI. You'll use it when wiring up CXProvider and CXCallController, handling incoming VoIP pushes with PushKit, or building Call Directory extensions for caller ID and blocking. The guide walks through the correct sequence for reporting calls, fulfilling actions in your provider delegate, and letting CallKit manage your audio session activation instead of doing it yourself. It targets Swift 6.3 and iOS 26+, includes the PushKit token registration flow, and has a mistakes section that should save you from the common pitfalls like reporting calls too late or activating audio at the wrong time.