WhatsApp for Lumia 900, Lumia 800, Lumia 710 and Lumia 610 is available on Windows Phone Store. This is version 2.8.2, this application utilizes push notifications to instantly get messages from friends, colleagues and family.
WhatsApp Messenger is a smartphone messenger available for Windows Phone, Android, BlackBerry, iPhone, and Nokia phones. WhatsApp uses your 3G or WiFi (when available) to message with friends and family. Switch from SMS to WhatsApp to send and receive messages, pictures, audio notes, and video messages. First year FREE! ($0.99/year after)
WhatsApp for Lumia is available free on Windows Phone Store.
Download | Windows Phone Store