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Voice AI API for agencies building phone agents

A client says yes and wants their phone agent live soon. Each build means wiring speech recognition, a language model, a voice and a carrier together, running a server for it, and then holding bills you have to pass on. For agencies and freelancers who build phone agents for businesses on a setup fee and a retainer. Each client gets their own Wixzel Voice account, in their name, and calls go over their own carrier account. One API key per client covers every voice engine, billed per second, with Indian languages on sarvam ($0.0617 per minute) and gemini-live ($0.0491).

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A lime key ring holding five keys, one for each client account

How do you build phone agents for your clients with Wixzel Voice?

  1. 01
    One account per client

    Open a Wixzel Voice account in each client's name. Its credit, numbers, calls, limits and API keys are its own. There are no team logins or sub-accounts yet, so you sign in to each account or keep an API key for each.

  2. 02
    POST /v1/agents/generate

    Make the first draft of the agent from the client's website: its name, prompt, opening line, knowledge base and mascot. Change any of it with PATCH /v1/agents/{id}.

  3. 03
    POST /v1/sip-trunks

    Connect the client's carrier account (Twilio, Telnyx, Plivo, Vonage, Bandwidth, Exotel, Vobiz or any SIP provider) so the agent answers the number they already have, or buy a new number on it with POST /v1/phone-numbers/purchase. The carrier bills the client directly.

  4. 04
    POST /v1/mcp-servers, PATCH /v1/webhook

    Connect the client's tools: apps like Cal.com, Calendly and Pipedrive that the agent uses during calls, and a signed webhook to their CRM or to Zapier, Make or n8n after each call.

  5. 05
    GET /v1/usage/summary

    The client's spend for any period, itemised in GET /v1/usage/events by speech, model, voice and orchestration fee. This is the cost you set the retainer against.

Which voice engine fits a client's phone agent?

Use the sarvam engine on Wixzel Voice, at $0.0617 per connected minute. Many clients' callers speak Hindi, Tamil, Malayalam or another Indian language, and sarvam is built for 11 Indian languages end to end. Where cost matters most, gemini-live is $0.0491 per minute and speaks 97 languages, Hindi, Tamil and Malayalam among them. Each client's agent can use a different engine.

What does a client's phone agent cost on Wixzel Voice?

Wixzel Voice engine time for 2-minute calls on the sarvam engine, at typical speech rates, billed per second of actual usage. Telephony is your own trunk at your carrier’s rate and is not included, and shorter calls cost proportionally less.

Calls per monthConnected minutesEngine cost per month
300600$37.02
1,0002,000$123
3,0006,000$370

Prepaid: add credit from $5 and the calls spend it. Estimate your own mix.

Which guides show how to build phone agents for your clients on Wixzel Voice?

AI phone call API

Four requests to a ringing phone, what a call record returns, and what a call costs.

Bring your own SIP trunk

Twilio, Telnyx, Plivo, Vonage, Bandwidth, Exotel, Vobiz or any SIP provider: what to set at the carrier.

Frequently asked questions

Can an agency build phone agents for its clients on Wixzel Voice?

Yes. Wixzel Voice is the API and MCP server you build the agents with. You create each client's agent, connect their carrier and their tools, and look after it. Wixzel Voice does not build agents for your clients and does not sell to them.

How do I run several clients?

Give each client their own Wixzel Voice account, in their name. Each account has its own credit, numbers, calls, API keys and concurrent-call limit (5 by default, raised on request). There are no team logins, sub-accounts or white-label console today, so you sign in to each account, or keep an API key for each and use it from your code or from Claude Code, Codex or Cursor.

Whose carrier account do the calls use?

The client's. Wixzel Voice connects to it over SIP, and the carrier bills the client for the number and the phone minutes at its own rate. You keep the client's existing number, or buy a new one on their carrier account through the API. You never hold the carrier bill.

What does a client's agent cost to run?

1,000 two-minute calls a month is 2,000 connected minutes: about 123 dollars on sarvam or 98 dollars on gemini-live, plus the carrier's rate. Calls are billed per second with no subscription, so a quiet month costs less. GET /v1/usage/summary gives the real figure for any period.

Can I show a client a working agent before they sign?

Yes. POST /v1/agents/generate makes an agent from the client's website. Talk to it in the console (each new account gets 5 free minutes of this), or send the client the agent's share link so they can talk to it from their phone. Share-link talks use credit like any web session, and no phone line is needed.

Who pays for the credit?

Whoever owns the account adds it, from $5, by card on the website. The client can add credit to their own account while you charge the setup and the retainer separately, or you can add it yourself and bill the client for it.

Can the client see their own calls?

Yes. The client signs in to their own account and sees every call with its summary and transcript, and who called. They can do the same in the Wixzel Voice app for Android, which is not on Google Play yet.

What else do agencies and developers build on Wixzel Voice?

Appointment booking

Build an agent that answers the phone, checks availability and books an appointment, over your own SIP trunk, with the booking written back through the API.

Outbound lead qualification

Upload leads, start a campaign, and have an agent call each one over your own SIP trunk and ask your qualifying questions. Every call is a record with its status and transcript, linked to the lead.

Inbound support line

Answer a support number with an agent that reads from a knowledge base you upload, handles the common questions, and leaves a transcript of every call.

Indian languages

Run phone agents in Indian languages on models built for them, with the sarvam engine covering speech-to-text, the language model and text-to-speech end to end.

Web and mobile apps

Put an agent in a browser page, a Flutter app or a kiosk with no SIP trunk and no phone number: your server mints a one-minute session, the app streams audio over a WebSocket, and the session is billed like a call.

Website voice assistant

Put a talking AI assistant on your website with one script tag: an agent made from your site, with an animated mascot visitors call from the browser, caller details, who-can-call settings and daily caps.

Phone calls from AI agents

Connect Claude Code, Codex, Cursor or any MCP client to your account, and let an AI agent connect a carrier, build a voice agent, place calls, run campaigns and read transcripts, with every tool that spends money asking first.

Low-cost AI calling

Run AI phone calls for a few cents a minute: per-second billing from prepaid credit, no subscription or minimum, your own SIP trunk with no telephony markup, and every charge itemised.

Talking AI avatar

Give a voice agent a face: an animated avatar that lip-syncs to the agent, for a website, a share link, a web app or a Flutter app, with no fee for the avatar.

All Wixzel Voice facts

Operator, prices, limits, refunds and data location, on one page.

Build your first voice agent

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