How to Call Real Phone Numbers from a Browser Using WebRTC and SIP

A developer guide explains how to connect browser-based WebRTC audio to the public telephone network (PSTN) using a SIP telephony provider such as Telnyx. The architecture involves three components: the browser capturing audio via WebRTC, a telephony provider bridging WebRTC to traditional phone infrastructure, and a backend server that issues short-lived credentials. A key security rule emphasized throughout is that API keys must never reach the browser — only a JWT token of limited duration is sent to the client. The guide also highlights non-obvious billing and timing quirks, such as zero-second calls appearing on invoices and CDR rounding mismatches. Virtual phone numbers can be purchased and configured programmatically via REST API as part of the same setup.