WhatsApp is one of the most used apps not only when it comes to messaging, but any app in general.  The app has seen several adding features since it has hit the Windows Phone store.  Now WhatsApp will see the added feature of notification tones.  You can have different tones for individuals and for group chats.

At the rate that WhatsApp has been seeing updates and added features you can look forward to more updates on the way in the near future.