SIP Trunking Overview

Plug your own voice infrastructure into Callr over SIP. Your PBX, SBC, call center or AI voice agent keeps doing what it does best, and Callr brings the rest: worldwide calling, phone numbers, programmable call flows, recording, transcription and AI.

flowchart LR
  PBX["Your PBX / SBC<br/>call center"] -- "SIP termination" --> Callr(("Callr"))
  Callr -- "PSTN" --> PSTN["Phone numbers<br/>worldwide"]
  Caller["Callers"] -- "Callr numbers" --> Callr
  Callr -- "dial@v2 (SIP / TLS)" --> SIP["Your SIP endpoints<br/>AI voice agents"]

Two directions, one platform

Send calls through Callr

SIP termination. Your PBX or SBC sends calls to Callr, and Callr delivers them to any phone number worldwide.

Receive calls on your SIP

Callr Actions. A call reaches a Callr number, your scenario routes it to your PBX, call center or AI agent with dial@v2.

SIP termination

Create a trunk group in the Console, under VoIP → SIP termination, then point your PBX or SBC to eu.sip.callr.com or usa.sip.callr.com.

Setting	What it does
Authorized IP addresses	Only calls from these IPs are accepted on the trunk group
SIP credentials	Optional username and password, checked in addition to the IP
Prefix	Shares one IP between several trunk groups or sub-accounts: send it before the number (`PREFIX#+33…`) or in the `X-Callr-Account-Code` header
Number format	The format your PBX uses for numbers
Channels / CPS	Maximum simultaneous calls and calls per second
Destination restrictions	The countries and destinations the trunk group can call

🚧
Emergency and special numbers
SIP termination trunks cannot be used for emergency services. Special numbers (toll-free, short numbers) are usually blocked by foreign carriers.

Calls to your SIP endpoints

Callr numbers ring a Callr Actions scenario. With dial@v2, the scenario sends the call to any SIP URI, over UDP, TCP or TLS, with failover between targets, call recording, transcription and everything else Callr Actions offers.

- action: dial@v2
  params:
    targets:
      - number: sip:[email protected];transport=tls
        timeout: 30

📘
SIP origination trunks
The legacy SIP origination trunks of the Console are being deprecated: use dial@v2 in a Callr Actions scenario instead.

Use cases

Keep your call center

Agents stay on your existing platform. Callr handles numbers, routing, tracking and recording.

Bring your own PBX / SBC

Keep your infrastructure and use Callr as your carrier and programmable voice layer.

Build AI voice agents

Route calls to a real-time AI agent, and transfer to a human when needed.

Connect any SIP system

Dial SIP URIs, transfer calls, or bridge conferencing and voice platforms.

Next steps

SIP Connectivity

Endpoints, IP ranges, INVITE format, codecs and call rejections.

Connect to OpenAI

Send calls to an OpenAI Realtime agent over SIP.

Connect to ElevenLabs

Send calls to an ElevenLabs agent over SIP.

Connect to Vapi

Send calls to a Vapi assistant over SIP.