Voice API is referred to as a tool that allows software developers to integrate calling features using an Application Programming Interface (API). Developers build a chat app with voice functionality and Voice APIs let these apps make and receive phone calls acting as a bridge to PSTN (Public Switched Telephone Network).

The four main standards of measuring a good Voice Chat API:
1. API features
2. Popularity 
3. Price
4. Ease of Use

We provided list of voice call/chat API and SDK providers are the few top one's from the ocean of many and also identify who are the approachable voice chat API providers in the market to build your voice calling app. 

Developers build a voice chat app with APIs let these apps make and receive phone calls acting as a bridge to PSTN (Public Switched Telephone Network).