SIP trunk

What it is

A SIP trunk is a virtual phone line over the internet. Instead of physical circuits, calls are set up with the Session Initiation Protocol and carried as audio packets. Voice-agent platforms accept calls in three main ways: you forward your existing number to a number they provide, you point a SIP trunk from your carrier or PBX at their platform (often called "bring your own carrier"), or you buy numbers from them directly.

The SIP route keeps your numbers, your carrier contracts and your call recording where they are, and lets you route only some calls (after hours, overflow, one queue) to the agent.

Why it matters when buying

Telephony is a real line in the all-in cost and a real source of latency and quality problems. Each extra hop (your carrier to your PBX to the agent's cloud in another country and back) adds delay and a chance of audio degradation. In some markets, carrier rules on number use, caller ID and recording differ, and the agent's platform may not have local numbers or local interconnect at all. Bring-your-own-carrier also determines who is responsible when calls fail.

What to ask

Ask which connection methods are supported and which the vendor recommends for your country. Ask where the media (the audio) is processed and how far it travels from your carrier. Ask about codec support (narrowband versus wideband), caller-ID handling and whether DTMF passes through. Ask for the per-minute telephony cost separately from the agent price, and who pays for inbound and outbound legs during a transfer.