Internal extensions: dial a colleague, free

What's new

If you have two or more devices registered to Sautikit (desk phones, an office PBX, softphones), they can now call each other by extension. Reception dials 1001 and the handset in the back office rings.

Calls between two of your devices by extension are free and do not appear in your call log.

Assigning one

An extension is a field on a SIP credential. Set it when you create the credential, or change it later:

await fetch(
  `https://api.sautikit.com/v1/numbers/${numberId}/sip-credentials`,
  {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.SAUTIKIT_API_KEY}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({ label: "Back office", extension: "1001" }),
  }
);

It is also in the console, on the SIP panel of any number: an Extension column in the credential list, and an editable field next to the name.

Changing an extension applies immediately and needs no change on the device. Pass an empty string to remove it.

Rules

• Unique per workspace. 1001 means one device, whichever of your numbers the credential belongs to. A clash returns numbers.extension_taken.
• Exactly four digits. Anything else returns numbers.extension_invalid.
• Optional. A credential without an extension still receives outside calls and can call out. Revoking a credential frees its extension for reuse.

Forwarding an outside call to a handset

An extension is also a valid forward destination, so an incoming call to your number can ring a desk phone:

{
  "forward": {
    "destinations": ["1001", "+254720000000"],
    "first_answer_wins": true
  }
}

You can mix extensions and phone numbers. Here the handset and a mobile ring together, and whichever answers first takes the call.

That call is logged and billed as a normal call. Only calls between two of your own devices are free.

If the device is off

The caller hears a short message.

API and MCP

• POST /v1/numbers/{id}/sip-credentials accepts extension
• PATCH /v1/numbers/{id}/sip-credentials/{credential_id} accepts extension (an empty string clears it)
• GET /v1/numbers/{id}/sip-credentials returns extension on each credential
• The create_sip_credential and update_sip_credential MCP tools take it too, with clear_extension on the update

See Numbers: internal extensions for the full reference.