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

- Inbound + outbound
- AI agents
- Unified call history
Trusted by developers at
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.
From number to live agent in three steps

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.

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.

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.
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
Jul 7, 16:15
+1 308 208 0660
+1 308 929 0284
Jul 7, 16:09
+1 308 208 0660
+1 330 960 7381
Calling history
Every call, inbound and outbound, lands in one place. Search and pull recordings whenever you need them.

Calls & Voicemail
OnNo 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.
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
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.
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