AI phone call API: place and answer real calls with an AI agent

What is the Wixzel Voice API for AI phone calls?

How do you place an AI phone call with Wixzel Voice?

1. 01

   Connect your SIP trunk

   Your carrier's host and credentials. The password is encrypted at rest and never returned again. The response carries platform_ip (95.216.218.102 today), which your carrier must allowlist, and origination_uri (sip:95.216.218.102:5090 today), where your carrier sends inbound calls.

   cURLCopy

   curl https://api.voice.wixzel.com/v1/sip-trunks \
     -H "Authorization: Bearer $WIXZEL_API_KEY" \
     -H "Content-Type: application/json" \
     -d '{
       "name": "My carrier",
       "host": "sip.carrier.example",
       "username": "acct123",
       "password": "..."
     }'

2. 02

   Register a phone number on it

   A number you already own at that carrier, in E.164. Wixzel Voice does not sell or port numbers.

   cURLCopy

   curl https://api.voice.wixzel.com/v1/phone-numbers \
     -H "Authorization: Bearer $WIXZEL_API_KEY" \
     -H "Content-Type: application/json" \
     -d '{
       "phone_number": "+14155550100",
       "sip_trunk_id": "'"$TRUNK_ID"'"
     }'

3. 03

   Create an agent

   A short spoken-style prompt, the first words it says, and a voice: three models, or one realtime model. opening_message is required, because an agent without one answers in silence. outbound_phone_number_id makes the number from step 2 its caller ID.

   cURLCopy

   curl https://api.voice.wixzel.com/v1/agents \
     -H "Authorization: Bearer $WIXZEL_API_KEY" \
     -H "Content-Type: application/json" \
     -d '{
       "name": "Support",
       "system_prompt": "You are a concise support agent.",
       "opening_message": "Hi, how can I help?",
       "voice": {
         "stt": { "model": "deepgram/nova-3" },
         "llm": { "model": "openrouter/gpt-4o-mini" },
         "tts": { "model": "elevenlabs/eleven_turbo_v2_5" }
       },
       "outbound_phone_number_id": "'"$NUMBER_ID"'"
     }'

4. 04

   Place the call

   A destination and an agent. Idempotency-Key is required, because a network timeout says nothing about whether the call was placed: retrying with the same key returns the original call instead of dialling twice. The response is 201 with the call, status: "queued".

   cURLCopy

   curl https://api.voice.wixzel.com/v1/calls \
     -H "Authorization: Bearer $WIXZEL_API_KEY" \
     -H "Idempotency-Key: $(uuidgen)" \
     -H "Content-Type: application/json" \
     -d '{
       "to": "+14155551234",
       "agent_id": "'"$AGENT_ID"'"
     }'

Before the first call connects, your carrier has to allowlist platform_ip. The carrier guides show where that setting lives on Twilio, Telnyx, Plivo, Vonage, Bandwidth, Exotel, Vobiz.

How do you place an AI phone call from TypeScript or Dart?

import { WixzelVoice } from 'wixzel-voice';

const client = new WixzelVoice({ apiKey: process.env.WIXZEL_API_KEY! });

// 1. Connect your SIP trunk.
const trunk = await client.sipTrunks.create({
  name: 'My carrier',
  host: 'sip.carrier.example',
  username: 'acct123',
  password: process.env.CARRIER_PASSWORD!,
});
console.log('Allowlist', trunk.platform_ip, 'and send inbound calls to', trunk.origination_uri);

// 2. Register a number you own on it.
const number = await client.phoneNumbers.create({
  phone_number: '+14155550100',
  sip_trunk_id: trunk.id,
});

// 3. Create the agent, with that number as its caller ID.
const agent = await client.agents.create({
  name: 'Support',
  system_prompt: 'You are a concise support agent.',
  opening_message: 'Hi, how can I help?',
  voice: {
    stt: { model: 'deepgram/nova-3' },
    llm: { model: 'openrouter/gpt-4o-mini' },
    tts: { model: 'elevenlabs/eleven_turbo_v2_5' },
  },
  outbound_phone_number_id: number.id,
});

// 4. Place the call. The SDK sends the Idempotency-Key for you.
const call = await client.calls.create({ to: '+14155551234', agent_id: agent.id });

// Inbound: calls to the number are answered by the same agent.
await client.phoneNumbers.update(number.id, { inbound_agent_id: agent.id });

// Later: what happened, what it cost, what was said.
const detail = await client.calls.retrieve(call.id);
console.log(detail.status, detail.cost_micros, detail.failure_code, detail.failure_reason);
for (const line of detail.transcript) console.log(line.role, line.content);

import 'dart:io';

import 'package:wixzel_voice/wixzel_voice.dart';

Future<void> main() async {
  final client = WixzelVoice(apiKey: Platform.environment['WIXZEL_API_KEY']!);

  // 1. Connect your SIP trunk.
  final trunk = await client.sipTrunks.create(CreateSipTrunk(
    name: 'My carrier',
    host: 'sip.carrier.example',
    username: 'acct123',
    password: Platform.environment['CARRIER_PASSWORD']!,
  ));
  print('Allowlist ${trunk.platformIp}; send inbound calls to ${trunk.originationUri}');

  // 2. Register a number you own on it.
  final number = await client.phoneNumbers.create(CreatePhoneNumber(
    phoneNumber: '+14155550100',
    sipTrunkId: trunk.id,
  ));

  // 3. Create the agent, with that number as its caller ID.
  final agent = await client.agents.create(CreateAgent(
    name: 'Support',
    systemPrompt: 'You are a concise support agent.',
    openingMessage: 'Hi, how can I help?',
    voice: VoiceConfig.composed(
      stt: const SttConfig(model: 'deepgram/nova-3'),
      llm: const LlmConfig(model: 'openrouter/gpt-4o-mini'),
      tts: const TtsConfig(model: 'elevenlabs/eleven_turbo_v2_5'),
    ),
    outboundPhoneNumberId: number.id,
  ));

  // 4. Place the call. The SDK sends the Idempotency-Key for you.
  final call = await client.calls.create(CreateCall(
    to: '+14155551234',
    agentId: agent.id,
  ));

  // Inbound: calls to the number are answered by the same agent.
  await client.phoneNumbers.update(
      number.id, UpdatePhoneNumber(inboundAgentId: agent.id));

  // Later: what happened, what it cost, what was said.
  final detail = await client.calls.retrieve(call.id);
  print('${detail.status} ${detail.costMicros} ${detail.failureCode}');
  for (final line in detail.transcript) {
    print('${line.role}: ${line.content}');
  }
  client.close();
}

How does an AI agent answer inbound calls on Wixzel Voice?

curl -X PATCH https://api.voice.wixzel.com/v1/phone-numbers/$NUMBER_ID \
  -H "Authorization: Bearer $WIXZEL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "inbound_agent_id": "'"$AGENT_ID"'" }'

What does a Wixzel Voice call record return?

What happens when an AI phone call does not connect?

What does an AI phone call cost on Wixzel Voice?

Prepaid: add credit from $5, no subscription and no free tier. The cheapest engine today is gemini-live at $0.0466 per minute. Estimate your own mix.

What are the limits of the Wixzel Voice API for AI phone calls?

• Wixzel Voice is in alpha, deployed and taking real calls. Behavioural changes ship behind a dated Wixzel-Version header, and an existing key keeps the behaviour it was created with.
• Five concurrent calls per account by default, raised on request. Web and app sessions count toward the same limit.
• Human transfer is blind only: the caller is handed straight to a number you listed. Attended transfer is not built, and transfer is unavailable on test calls and in web or app sessions.
• Wixzel Voice does not sell or port phone numbers, and phone calls need your own SIP trunk.
• Web and app sessions carry G.711 µ-law audio at 8 kHz, which is phone quality, not wideband.
• 10 API requests per second per key, with a burst of 20. A rate-limited request is never charged.
• The API and stored data are in Helsinki, Finland. Speech and language providers in the United States and India process audio and text for the duration of a call; the sarvam engine processes speech in India.
• No free tier and no trial credit. The minimum top-up is $5.

Frequently asked questions

What is an AI phone call API?

An API that connects an AI agent to a real phone call: your code names a number and an agent, and the API dials, runs the conversation with speech recognition, a language model and speech synthesis, and returns the call's status, its transcript and its cost. Wixzel Voice is one: POST /v1/calls places a call over your own SIP trunk, and a phone number with an inbound_agent_id answers calls the same way.

Is Wixzel Voice an AI calling API or a finished calling agent?

An API. You build the agent: its prompt, its opening line, its voice engine and what your system does with the result. Wixzel Voice sells the APIs, the SDKs and the MCP server, and never a finished agent.

How much does an AI phone call cost?

The voice engine costs $0.0867 per connected minute on classic, $0.0623 per connected minute on sarvam, $0.0466 per connected minute on gemini-live, $0.1851 per connected minute on deepgram-agent, each including the $0.012 orchestration fee, billed per second of actual usage. A three-minute call on classic is about $0.2601. Your carrier bills the phone line separately, at your rates, with no markup.

Can the AI agent answer inbound calls as well as place outbound ones?

Yes. Set inbound_agent_id on a phone number with PATCH /v1/phone-numbers/{id} and calls to that number are answered by that agent. Your carrier has to send inbound calls to the origination_uri the trunk returns. Without an inbound_agent_id, inbound calls to the number are rejected.

Can the AI agent transfer a caller to a person?

Yes, as a blind transfer: when a caller asks for a person, the agent hands the live call to one of the destinations you listed on the agent in human_transfer, dialled over your SIP trunk. Attended transfer, where the agent speaks to the person first, is not built, and transfer is unavailable on test calls and in web or app sessions.

How many AI calls can run at once?

Five concurrent calls per account by default, raised on request. A call over the limit is refused before anything is dialled and costs nothing. Web and app sessions count toward the same limit.

Is there a free trial?

No. The API is prepaid, with a $5 minimum top-up and no subscription. A call that cannot fund its first 15 seconds is refused with 402 insufficient_credits before anything is allocated.

Where to go next