WhatsApp introduced voice calling in 2015.
Voice calls between WhatsApp accounts were added during March and April 2015, expanding the service beyond text and multimedia messaging. The rollout initially reached Android users and then spread to other supported platforms. Because calls used an internet connection rather than a traditional mobile network, they became especially useful for people making international calls or communicating in places with expensive phone rates.
This feature is sometimes confused with voice messages. WhatsApp had already added voice messages in August 2013; those are short recordings sent inside a chat. Voice calling is a live, two-way conversation, similar to a conventional phone call but routed through the internet.
WhatsApp later extended the calling system with video calling in November 2016 and group audio and video calls in 2018. By June 2016, WhatsApp reported that users were placing more than 100 million voice calls per day, showing how quickly the feature became a major part of the app.