What is Whatsapp?
Its a cross platform instant messenger, think SMS/BBM.
It works on iPhone, Android, Blackberry and Nokia. Currently BBM is restricted to Blackberries only.
It offer messages, videos, photos, audios and more.
No cost of sending messages because it uses your data connection. You can use WiFi or 3G. A world of caution: if you have a limited data plan or on roaming, you may be paying for sending messages.
Sounds too good to be true? Now the fine print Its a paid app, on no! For iPhone its $.099 and for Android its free for first year after that its $2.
Its still worth it. Enjoy Whatsapp.