A voice API is a tool used by app developers use to make and answer calls through an interface (API) for their programs. It helps connect apps that work on internet to the regular phone network. Call conferencing, Audio playback, Call recording, Audio Streaming, and Programmable SIP are some of the voice call features that are essential for any enterprise app.

You can also add features like Speech Synthesis Markup Language (SSML), call queuing, routing, and audio encryption depending on your business model and user requirements.