If you want to install WhatsApp Messenger on YouWave. You can check this instruction below.
"WhatsApp Messenger is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for iPhone, BlackBerry, Android and Nokia and yes, those phones can all message each other! Because WhatsApp Messenger uses the same internet data plan that you use for email and web browsing, there is no cost to message and stay in touch with your friends.
In addition to basic messaging iPhone, Android, Nokia and BlackBerry WhatsApp Messenger users can send each other unlimited images, video and audio media messages."
Or if you want to know more about this application, you can this video :