General • Last Updated 5/17/2024

How call control is changing communication

The complete guide to Call Control. Explore the Telnyx Programmable Voice API, and what you can build with it.

By Pete Christianson

Feature Call Control Explained

What is Call Control?

Call Control is an API built by Telnyx that allows you to control phone calls with code. Businesses all over the world use Call Control to build contact center applications, call tracking tools, conversational AI and voice analytics programs, and more.

When we first built our Programmable Voice API, we named it Call Control in honor of a classic telephony concept, calling on our years of telephony experience and our global Tier-1 telephony network.

Voice APIs allow you to make, manage and route calls globally to any device — phone, app or browser. At Telnyx, we go several steps further, enabling real-time media analysis, answering machine detection and advanced conferencing, among a plethora of other powerful features.

Watch this short video to get an overview of the Telnyx Voice API and what you can build with it:

How Call Control Works

The Call Control framework is essentially a set of REST APIs that allow you to control your call flows, from the moment a call comes in (or out), to the moment you terminate that call. In between, you’ll receive a number of webhooks for each step of the call, which you answer with a command. It's this communication back and forth that provides you with uniquely granular control over your calls.

There are plenty of features available with Call Control, which gives you a highly customizable experience.

  • Play audio recordings like hold music, advertising, announcements or prompts
  • Gather inputs from the user via keypad or voice
  • Dynamically display a custom caller ID
  • Dual channel call recording and long term storage
  • Text-to-speech, available in 28 accents across various languages
  • Answering machine detection

In-Depth Call Control Features

Real-time Media Streaming

Get instant access to your raw call media. The moment the call is established, Telnyx takes the call media and forks it, so recipients receive the call simultaneously. Our network ensures that call media can be duplicated, delivered, analyzed and returned in real time. And the second recipient never occupies the call stream, so you never have to worry about degraded quality or dropped connections.

Using Media Forking, you can build next-gen features into your application, like sentiment analysis, call transcriptions and voice biometrics.

Global Audio Conferencing

Call Control makes it easy to embed feature-rich audio conferencing into your applications. So you can connect people and teams wherever they are in the world, with granular, real-time control over your conferencing experience.

Using conferencing, you can specify hosts that control global conference behavior, play sounds when participants join and leave, define a length of time after which the conference automatically ends, mute and unmute or hold and unhold participants, and much more.


Call Control supports advanced Text-to-Speech (TTS) out-of-the-box, so you can play-back customized, personalized messages to your callers. We leverage Amazon Polly for high-quality dynamic TTS in multiple languages and accents. It’s incredibly easy to set up this basic building block of intelligent call flows with Telnyx - our video guide has copy-and-paste code that you can set up in just five minutes!

Answering Machine Detection

Call Control features Answering Machine Detection (AMD), informing you whether a machine or a human answered your automated outbound call. This enables a huge range of efficiencies for sales teams, outbound interactive voice response (IVR) systems, and automated text-to-speech announcement calls. Our intelligent algorithms identify answering machines in real-time with industry-leading 97% accuracy, allowing you to drive better results in your outbound calls.

Agent Coaching

Call Control allows you to manage call flows and participants in innovative ways. In contact centers, coaches can speak to agents privately, without being heard by the other party on the call, opening up possibilities for real-time coaching and guidance. This functionality can be extended to a pre-answer whisper for inbound calls - giving your agents an audible heads-up about who’s calling, so they answer the phone fully prepared to provide the best possible customer experience (CX).

Audio Playback

Call Control allows you to play and manipulate custom media at any point in a call or in response to actions by either call party. From pre-recorded instructions and prompts to custom hold music or even promotional messages, this capability can vastly improve your CX on inbound calls, especially in conjunction with a cloud IVR system to automate your inbound call handling.

Call Recording

With Call Control, recording calls has never been easier. High-quality call recording is available on-demand on both inbound and outbound calls. Recording can be configured per number or per settings profile for a group of numbers. Configuration can also be done by API commands. What’s more - your recordings are stored securely in the cloud with easily searchable time-stamps.

Smart IVR

Call Control empowers you to build smart interactive voice response (IVR) systems, automating large parts of your inbound call handling for better efficiency and smoother CX. Our smart call routing, media playback and input gathering features allow you to build an IVR that works for your business, at a cost that works for your bottom line.

What can you build with Call Control?

Today, the Telnyx voice API is used by a diverse set of enterprise applications, including contact center, conversational AI, inbound call tracking, unified communications and sales acceleration platforms. With it you can build:

Getting Started with Call Control

The best way to get started is to head to our Developer Center and follow our Call Control Quickstart guide. Here, you'll also be able to leverage SDKs and guides in popular programming languages including Python, Ruby and Node, with more on the way. We also have video guides walking you through the whole process in just a few minutes.

Call Control Docs for Developers

Integrating Twilio TwiML Conference on Telnyx:

Telnyx Conference System Demo:

Additional Call Control Developer Documentation:

If you need any help getting set up, you can reach our community of Product Managers and Engineers via our developers slack channel anytime. Just head to:

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