CallKit Build VoIP calling features that integrate with the native iOS call UI using CallKit and PushKit. Covers incoming/outgoing call flows, VoIP push registration, audio session coordination, and call directory extensions. Targets Swift 6.3 / iOS 26+. Contents - Setup - Provider Configuration - Incoming Call Flow - Outgoing Call Flow - PushKit VoIP Registration - Audio Session Coordination - Call Directory Extension and Manager - Common Mistakes - Review Checklist - References Setup Project Configuration 1. Enable the Voice over IP background mode in Signing & Capabilities 2. Add the Push…