Over the past year, we've been progressively rolling out Signal Protocol support for all WhatsApp communication across all WhatsApp clients. This includes chats, group chats, attachments, voice notes, and voice calls across Android, iPhone, Windows Phone, Nokia S40, Nokia S60, Blackberry, and BB10.
As of today, the integration is fully complete. Users running the most recent versions of WhatsApp on any platform now get full end to end encryption for every message they send and every WhatsApp call they make when communicating with each other. This includes all the benefits of the Signal Protocol - a modern, open source, forward secure, strong encryption protocol for asynchronous messaging systems, designed to make end-to-end encrypted messaging as seamless as possible.
WhatsApp is the most popular messaging protocol in the world (in my own country it's effectively at 100% market share), so to see it do end-to-end encryption is a huge deal.