twilio-voice-outbound-calls

Overview

Agent safety: Before placing an outbound call, always confirm the recipient number and intent with the user. Outbound calls are irreversible and may incur charges. For automated systems, implement TCPA compliance: obtain prior express consent, respect quiet hours (8 AM–9 PM recipient local time), and maintain a Do Not Call list.

Every outbound call requires a from Twilio number, a to recipient, and TwiML instructions that define what happens when the call is answered — either as a webhook URL or inline.

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Voice Platform Capabilities

Outbound calls go beyond basic calls.create(). Here's what you can build:

Capability	How	When to use
Basic outbound call	calls.create() with TwiML or webhook URL	Any outbound call — see Quickstart below
Answering Machine Detection (AMD)	machineDetection parameter on calls.create()	Sales dialers, call campaigns — filter voicemail from humans
Conference-based agent bridging	<Dial><Conference> in TwiML	Connect agents to live prospects with whisper, barge, hold
SIP Trunking	Elastic SIP Trunking	Bring your own carrier for outbound calls — cost reduction at scale
Call Recording	record=True on calls.create() or <Record> verb	Compliance, QA, training
Voice Insights	Automatic per-call metrics	Call quality monitoring — latency, jitter, packet loss, answer rates
AI Voice Agents	ConversationRelay + LLM	Real-time speech recognition → LLM → TTS for conversational AI

For TwiML verbs (Say, Gather, Dial, Record, Conference, Pay), see twilio-voice-twiml. For AI voice agents, see twilio-voice-conversation-relay.

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Prerequisites

• Twilio account with a voice-capable phone number — New to Twilio? See twilio-account-setup for signup, getting a number, and trial limitations — Trial accounts can only call verified numbers
• Environment variables:
  • TWILIO_ACCOUNT_SID
  • TWILIO_AUTH_TOKEN — See twilio-iam-auth-setup for credential setup and best practices
• SDK: pip install twilio / npm install twilio

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Quickstart

Python

import os
from twilio.rest import Client

client = Client(os.environ["TWILIO_ACCOUNT_SID"], os.environ["TWILIO_AUTH_TOKEN"])

call = client.calls.create(
    from_="+15017122661",    # Your Twilio number (E.164)
    to="+15558675310",       # Recipient (E.164)
    twiml="<Response><Say>Your order has shipped. Goodbye.</Say></Response>"
)

print(call.sid)     # CAxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
print(call.status)  # queued | ringing | in-progress | completed | failed

Node.js

const twilio = require("twilio");
const client = twilio(process.env.TWILIO_ACCOUNT_SID, process.env.TWILIO_AUTH_TOKEN);

const call = await client.calls.create({
    from: "+15017122661",
    to: "+15558675310",
    twiml: "<Response><Say>Your order has shipped. Goodbye.</Say></Response>",
});

console.log(call.sid);
console.log(call.status);

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Key Patterns

Use a Webhook URL for Dynamic Call Handling

Pass a url instead of inline twiml — Twilio POSTs to your server when the call connects and executes the TwiML you return.

Python

call = client.calls.create(
    from_="+15017122661",
    to="+15558675310",
    url="https://yourapp.com/twiml/welcome"
)

Node.js

const call = await client.calls.create({
    from: "+15017122661",
    to: "+15558675310",
    url: "https://yourapp.com/twiml/welcome",
});

Python (Flask) — TwiML webhook handler

from flask import Flask
from twilio.twiml.voice_response import VoiceResponse

app = Flask(__name__)

@app.route("/twiml/welcome", methods=["POST"])
def welcome():
    response = VoiceResponse()
    response.say("Hello! Press 1 to hear your account balance.")
    response.gather(num_digits=1, action="/twiml/handle-input")
    return str(response)

Node.js (Express) — TwiML webhook handler

const { VoiceResponse } = require("twilio").twiml;

app.post("/twiml/welcome", (req, res) => {
    const response = new VoiceResponse();
    response.say("Hello! Press 1 to hear your account balance.");
    response.gather({ numDigits: 1, action: "/twiml/handle-input" });
    res.type("text/xml").send(response.toString());
});

For all TwiML verbs (Say, Gather, Dial, Record, Conference), see twilio-voice-twiml.

Track Call Status

Python

call = client.calls.create(
    from_="+15017122661",
    to="+15558675310",
    url="https://yourapp.com/twiml/welcome",
    status_callback="https://yourapp.com/call-status",
    status_callback_method="POST"
)

Node.js

const call = await client.calls.create({
    from: "+15017122661",
    to: "+15558675310",
    url: "https://yourapp.com/twiml/welcome",
    statusCallback: "https://yourapp.com/call-status",
    statusCallbackMethod: "POST",
});

Status transitions: queued → ringing → in-progress → completed (or failed/busy/no-answer).

Record a Call

Python

call = client.calls.create(
    from_="+15017122661",
    to="+15558675310",
    url="https://yourapp.com/twiml/welcome",
    record=True,
    recording_status_callback="https://yourapp.com/recording-ready"
)

Node.js

const call = await client.calls.create({
    from: "+15017122661",
    to: "+15558675310",
    url: "https://yourapp.com/twiml/welcome",
    record: true,
    recordingStatusCallback: "https://yourapp.com/recording-ready",
});

Recordings accessible at https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Recordings.

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Answering Machine Detection (AMD)

Detect whether a human or voicemail answers before connecting an agent or leaving a message. Two modes:

Mode	Behavior	Best for
Enable	Returns result immediately when human/machine first detected	Sales dialers — connect agent to humans ASAP
DetectMessageEnd	Waits for voicemail greeting to finish (beep/silence)	Leaving voicemail — wait for beep, then play/record message

Python — Sales dialer (connect agents to live answers only)

call = client.calls.create(
    from_="+15017122661",
    to="+15558675310",
    url="https://yourapp.com/handle-answer",
    machine_detection="Enable",  # Immediate detection — use for live-agent connect
    async_amd=True,              # Non-blocking — call connects while AMD analyzes
    async_amd_status_callback="https://yourapp.com/amd-result",
    async_amd_status_callback_method="POST"
)

Node.js

const call = await client.calls.create({
    from: "+15017122661",
    to: "+15558675310",
    url: "https://yourapp.com/handle-answer",
    machineDetection: "Enable",
    asyncAmd: true,
    asyncAmdStatusCallback: "https://yourapp.com/amd-result",
    asyncAmdStatusCallbackMethod: "POST",
});

AMD webhook delivers AnsweredBy parameter:

Value	Meaning	Action
human	Live person detected	Connect to agent
machine_start	Machine detected, greeting still playing	Hang up or wait
machine_end_beep	Voicemail beep heard	Leave message
machine_end_silence	Silence after greeting	Leave message
fax	Fax tone detected	Hang up
unknown	Could not determine	Treat as human or retry

Conference-based agent bridging (production pattern for sales dialers):

# In /handle-answer webhook — when AMD says "human":
response = VoiceResponse()
dial = response.dial()
dial.conference(
    f"Sales-{call_sid}",
    start_conference_on_enter=False,  # Prospect waits for agent
    end_conference_on_exit=True
)

# Separately, dial agent into same conference:
client.calls.create(
    from_="+15017122661",
    to=agent_number,
    twiml=f'<Response><Dial><Conference startConferenceOnEnter="true">Sales-{call_sid}</Conference></Dial></Response>'
)

This pattern gives you call control (whisper to agent before connecting, supervisor barge-in, hold) that direct <Dial> does not.

Cost: AMD adds ~$0.0075 per call to standard voice pricing.

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Response Fields

Field	Description
sid	Call identifier (CA...)
status	queued, ringing, in-progress, completed, failed, busy, no-answer
duration	Length in seconds (after completion)
price	Cost (populated after completion)

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Common Errors

Code	Meaning	Fix
21211	Invalid to number	Validate E.164 format
13224	Invalid TwiML at webhook URL	Validate TwiML response from your server
13225	TwiML URL returned non-200 status	Fix your webhook endpoint

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CANNOT

• Cannot use a private TwiML URL — Must be publicly accessible. Use ngrok for local development only; deploy to a cloud provider for production.
• Cannot exceed ~4,096 characters in inline twiml parameter — Use a TwiML URL for longer responses
• Cannot call unverified numbers on trial accounts — Upgrade to paid or verify recipient numbers first
• AMD accuracy is ~85-90% — Expect some false positives/negatives. Tune machineDetectionSpeechThreshold (default 2400ms) based on your results.
• AMD adds latency — Enable mode returns results faster but may misclassify short greetings. DetectMessageEnd is more accurate but adds seconds before your app can act.
• Cannot use AMD with SIP Trunking — AMD is only available on calls made via the Calls API

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Next Steps

• TwiML verb reference (Say, Gather, Dial, Record, Conference, Pay): twilio-voice-twiml
• AI voice agents with real-time speech/LLM: twilio-voice-conversation-relay
• Improve answer rates (Branded Calling, STIR/SHAKEN): twilio-numbers-senders