> ## Documentation Index
> Fetch the complete documentation index at: https://docs.buildwithchirp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Calling Overview

> Learn about making and receiving phone calls with Chirp

Chirp provides APIs for making and receiving phone calls, with support for PSTN, WebRTC, and WhatsApp channels.

## Getting Started

<CardGroup cols={1}>
  <Card title="Making Calls" icon="phone-arrow-up-right" href="/calling/making-calls">
    Initiate outbound calls to any phone number or channel
  </Card>

  <Card title="Receiving Calls" icon="phone-arrow-down-left" href="/calling/receiving-calls">
    Handle inbound calls with webhooks and call commands
  </Card>

  <Card title="Call Commands" icon="sliders" href="/calling/call-commands">
    Control active calls with answer, hold, transfer, and more
  </Card>

  <Card title="Recordings" icon="circle-dot" href="/calling/recordings">
    Record calls and access recording files
  </Card>

  <Card title="Voicemails" icon="voicemail" href="/calling/voicemails">
    Access and manage voicemail messages
  </Card>

  <Card title="Webhooks Setup" icon="webhook" href="/calling/webhooks-setup">
    Configure webhooks for real-time calling event notifications
  </Card>
</CardGroup>

## Channels

Chirp supports three calling channels. You can make calls within the same channel or across different channels.

**PSTN**

Traditional phone network calls. Use standard E.164 phone numbers to call landlines and mobile phones worldwide.

**WebRTC**

Browser and app-based calling over the internet. Enables real-time voice communication without a traditional phone line.

**WhatsApp**

Voice calls over WhatsApp. Reach users on WhatsApp using their phone number as the identifier.

<Info>
  Cross-channel calls are supported. For example, you can initiate a call from a WebRTC client to a PSTN phone number, or from a PSTN number to a WhatsApp user.
</Info>

## Prerequisites

Before you start making and receiving calls, you need:

* An application with calling enabled
* A phone number assigned to your application
* An API key for authentication (`sk_live_app_*` or `sk_test_app_*`)

See [Managing Phone Numbers](/sms/managing-numbers) to assign a number to your application.