Setup

Setup

A number you buy comes with PSTN calling on, so "setup" here is really about inbound routing: where an incoming call goes, plus voicemail, hours, and menus. It is one endpoint: enableVoiceOnNumber (POST /v1/phone-numbers/{id}/voice).

Set the forward destination

Inbound calls route to forwardTo, which accepts three destination types:

• tel:+E164 - a regular phone number
• sip:... - a SIP endpoint
• wss://... - a WebSocket media server, which is how you bridge to an AI voice agent (Vapi, Retell, or your own)

const { data } = await zernio.voice.enableVoiceOnNumber({
  path: { id: 'PHONE_NUMBER_ID' },
  body: {
    forwardTo: 'tel:+13105551234',
    recordingEnabled: false,
    transcriptionEnabled: false,
  }
});
console.log('Voice enabled:', data.enabled);

response = client.voice.enable_voice_on_number(
    id='PHONE_NUMBER_ID',
    forward_to='tel:+13105551234',
    recording_enabled=False,
    transcription_enabled=False,
)
print('Voice enabled:', response['enabled'])

curl -X POST "https://zernio.com/api/v1/phone-numbers/PHONE_NUMBER_ID/voice" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"forwardTo": "tel:+13105551234", "recordingEnabled": false, "transcriptionEnabled": false}'

Optional inbound features

Pass any of these alongside forwardTo to shape how inbound calls behave:

See enable voice on a number for each feature's exact field names and shapes.

How the features interact

The features aren't independent switches — an inbound call walks through them in a fixed order:

• Blocklisted callers get a busy signal. The call is rejected before it's answered — no charge, no voicemail, and no webhook fires for it.
• Business hours gate everything live. Outside the configured windows the call skips the menu and the forward entirely and goes to voicemail. With voicemail disabled too, it simply hangs up.
• The IVR menu supersedes the plain forward. When a menu with options is enabled, the caller hears it instead of ringing forwardTo directly; the pressed digit picks that option's destination. No or invalid input ends the call.
• Voicemail is the fallback for every non-answer. Unanswered forwards (about 25 seconds of ringing), failed bridges, and after-hours calls all land there: the greeting (yours, or a default) plays, a beep follows, and up to two minutes are recorded. You get an email, and the recording and transcript (when transcription is on) land on the call record — there is no separate voicemail webhook.
• Recording never starts silently. On bridged calls a consent notice plays first; the recording lands on the call record shortly after hangup, not on the call.ended payload.
• Webhooks: call.received fires as the call enters the pipeline (after the blocklist check, before any menu or ring), and every answered path ends with call.ended.

Turn voice off

Disable calling on a number with disableVoiceOnNumber (DELETE /v1/phone-numbers/{id}/voice). Settings are preserved so you can re-enable without reconfiguring.

curl -X DELETE "https://zernio.com/api/v1/phone-numbers/PHONE_NUMBER_ID/voice" \
  -H "Authorization: Bearer YOUR_API_KEY"

Next steps

• Bridge to an AI voice agent
• Place outbound calls
• Call from the browser