I manage enterprise Voice AI deployments and recently wrote a detailed breakdown of this decision: https://www.voiceaipm.com/2026/04/webrtc-vs-sip-which-protocol-for-your.html The short version of what I've found in production: If users call from a real phone number (mobile/landline): you need SIP. No way around it - the PSTN speaks SIP. If the voice interface lives in a browser (click-to-call, web widget): WebRTC. Opus codec, no carrier cost, NAT traversal handled automatically. Enterprise...