WhatsApp (Size: 8.08 MB)
A free online messaging application for Android OS. Also available for Symbian, iOS and Blackberry smartphones.
Note: The receiver of your messages should also have WhatsApp installed on their smartphone with their phone number registered.
Android OS 2.1 or above
Unlimited internet data plan recommended as the application syncs your messages in background. You can even turn off sync in 'Accounts and Sync' menu in settings.