Voice Call API

Enable calling on your number and route inbound calls to Vapi, Retell, or your own AI agent.

Remind MeMessage
DeclineAccept
AddKeypadMute
+1 (415) 555-0142
AI Agent
Calling
AI Agent
0:00
RecordingTranscribing
  • Inbound + outbound
  • AI agents
  • Unified call history

Trusted by developers at

Use cases

Voice API that works where you need it

Forward to a phone

Mon–Fri

AI Agent

Vapi

Voicemail

After hours

Inbound calling

Route every incoming call where it needs to go: an AI agent, a real phone, or a menu that gets callers to the right place. Add voicemail and business hours so nothing goes unanswered.

+1 (415) 555-0142

Calling

POST /v1/voice/calls

to+1 415 555 0142

fromNumber+1 618 575 1022

forwardTowss://zernio.com

200 dialing · call_8f2a

Outbound calling

Place calls straight from your app with one API call. Reach customers, trigger reminders, or connect them to an agent, all tracked automatically.

www.zernio.com

Sales team

Online now

Mon–Fri · 9–18

Call now

Browser calling

Let people call right from your web app, no phone needed. Just a browser, a click, and a live call.

How It Works

From number to live agent in three steps

1

Number ready

Your new phone is set up.

Number ready

+1 618 575 1022 is yours.

Done

Get a number

Buy or port a phone number. Calls are on by default the moment it's provisioned.

2

When someone calls

Send to voicemail

Inbound calls leave a message you can play back.

Forward incoming calls

To an AI agent (Vapi / Retell) or your own PBX.

Forward calls to

Custom SIP URI

SIP URI

sip:+16185751022@sip.zernio.com

Set where calls go

Zernio provides the Voice API, and you decide where calls go: a phone, SIP, or an AI agent.

3

New call

Call any number from one of your numbers.

Connected

Hang up

Call or get called

Make and receive calls, then manage them all in one place with optional call recordings.

Features

Build voice applications with flexible APIs

Inbound call rules

Business hours

Mon–Fri · 9:00–18:00

Outside hours

Voicemail

Blocked numbers

3

Rules run in order — the first match wins.

Inbound call rules

Send calls to voicemail, forward only during business hours, or block specific numbers. Set the rules once and calls follow them.

Destination

Per minute

5 min call

+1 415 555 0142

$0.010

$0.05

+44 20 7946 0958

$0.035

$0.18

+34 612 345 678

$0.046

$0.23

+52 55 1234 5678

$0.058

$0.29

Cost estimation before dialing

Check the per-minute rate for a destination before you dial, so you always know what a call will cost.

Search number…

All channels

All directions

Started

From

To

Channel

Jul 7, 16:15

+1 308 208 0660

+1 308 929 0284

PSTN

Jul 7, 16:15

+1 308 208 0660

+1 308 929 0284

PSTN

Jul 7, 16:09

+1 308 208 0660

+1 330 960 7381

PSTN

Calling history

Every call, inbound and outbound, lands in one place. Search and pull recordings whenever you need them.

Calls & Voicemail

On

No forward set — inbound calls go to voicemail.

Call recording on

Transcription on

Voicemail on

Call settings

Turn off calls

Recording & transcription

Turn on recording and get a written transcript for every call, so nothing important gets lost or forgotten.

Ways to integrate

Calling API built for developers

Call it from Node, Python, Go, Ruby, Java, PHP, .NET, or Rust, or the raw REST API and CLI.

Node

import Zernio from '@zernio/node';
const zernio = new Zernio(); // reads ZERNIO_API_KEY
const { data } = await zernio.voice.createVoiceCall({
  fromNumber: '+14155550100',
  to: '+13105551234',
  greeting: 'Connecting you now.',
});

console.log(data.status); // dialing
✓ 200 · dialing

Let an agent place the call

Point Claude, Cursor, or any MCP client at Zernio. It picks a number, sets routing, and dials, no dashboard.

MCP server

Claude Code v2.1.19

Opus 4.5 · Claude Max

~/software

✓ voice enabled · forwardTo wss://…

✓ greeting set · recording off

✓ outbound call dialing · id call_8f2a

Webhooks

Know the moment a call starts or ends

Subscribe to call lifecycle events. Same shape for PSTN and WhatsApp. Missed a call? Text them back on the linked conversation.

Read the docs
EventDescription
call.receivedInbound call routed, or outbound WhatsApp call placed
call.endedDuration, end reason, and cost breakdown
call.failedHard error before or during the bridge
call.permission_requestWhatsApp call permission accepted or rejected
Pricing

Pay for the minutes you use

No setup fees and no monthly minimums. Recording and transcription are billed only for the calls you turn them on for.

Call minutes starting at

$0.010

per min

Recording

+$0.004 / min (optional)

Transcription

+$0.03 / min (optional)

Frequently Asked Questions

Give your AI agent a phone number today

Get a number, point it at your agent, and take the first call.

  • Inbound + outbound
  • AI agents
  • Unified call history