Voice overview

Bird Voice lets you place calls to phone numbers and answer calls made to numbers you hold. Connect a phone system over SIP, place a browser call, or use the sequence builder to run a saved call flow. Bird connects calls to the public telephone network, the PSTN.

The connection between your phone system and Bird is a SIP trunk. SIP (Session Initiation Protocol) sets up calls between phone systems. Bird gives your workspace a trunk address, which your phone system uses for outbound calls to the telephone network, and which Bird uses in reverse to deliver the calls arriving on your numbers.

You do not need a phone system to make the first call: the phone in the dashboard places one straight from the browser, over one of your trunks.

You can also build a sequence in the dashboard and start it with the Create Call API. The sequence handles prompts, keypad choices, and call routing after the recipient answers.

How a call is placed

Your phone system sends a SIP INVITE to the trunk address to start a call. Bird checks the caller ID, destination country, limits, and wallet balance before contacting a carrier. If the call passes, Bird routes it and relays the audio. Each connection is a leg. When a leg ends, Bird writes its record under Voice > Legs and emits a voice_call.ended event.

A call that fails a check is refused before a carrier is involved, and the specific reason goes onto the leg record. Placing calls covers what Bird reads off each call, and Rejected calls lists every refusal reason and what to do about it.

How an incoming call is answered

A number your workspace holds carries one answer at a time, set on the number itself: deliver the call to one of your SIP trunks, forward it to a number you have verified, run a published sequence, or reject it. Every number starts on reject, so a number nobody has configured turns callers away.

When a call arrives, Bird checks the account limits and the wallet the same way it does for a call you place, then acts on the number's answer and records what that answer was on the call. Receiving calls covers pointing a number at an answer, what a forward presents to whoever picks up, and how to read a refusal.

Before your first call

For calls through your own SIP equipment, prepare the following. API calls follow the Create Call prerequisites.

1. Create a SIP trunk, turn outbound calling on, and allow callers on it: an IP range or an API key for your own equipment, session credentials for a browser or the CLI.
2. Choose an eligible caller ID: use a number your workspace holds through Bird, or register an external number and confirm it with a verification call.
3. Enable your destinations: turn on the countries you call.

Place your first call walks through all three requirements and ends with a real call.

Reading call records requires voice:read; placing calls requires voice:write. Managing trunks, number routes, caller IDs, and sequences uses voice_management permissions. Access to a page does not grant permission to change its settings or place a billable call.

The Voice app in the dashboard

Visibility

A call can contain multiple legs. The log has one record per leg, whether it connected, rang out, or was refused. Forwarded or multi-party calls can therefore have several entries:

• Leg log: the per-leg view on the Legs page. Status, both numbers, the trunk the leg came in on, the SIP response it ended on, answer and end times, billable time, and cost. Filter it, then export the result as CSV.
• Voice events: voice_call.initiated, voice_call.answered, and voice_call.ended delivered to your own endpoint, so your systems learn about a call without polling.

The API reference lists the supported public HTTP contracts and SDK methods. The CLI reference and MCP tool reference describe their published operations. These surfaces can expose different operations; a dashboard action or CLI command does not by itself establish a public SDK method.

Limits

Three ceilings apply to your calls, in both directions: how many you may have in progress at once, how many new calls per second, and what you may spend on voice in a UTC day. Each is set per organization, and the amounts depend on your plan. A call over any of them is refused at setup, and its record names which one, under Rejected calls.

The per-second ceiling is the voice_call policy in Rate limits, which also explains how your effective limit is resolved and how to request more capacity.

Next steps