Whatsapp messenger is an instant messaging application for mobiles through which users can send SMS free of charge to their fellow Whatsapp users anywhere in the world. This messenger uses the phone’s internet connection and saves the cost of a local/international SMS. It can also send attachments like photos, text files. I use this messenger to mainly SMS my friends from other countries. This messenger is like any other messenger and it runs at the background as soon as your mobile is on. It combines the features of SMS service and online chat. This messenger is free and can be downloaded here. Supported mobiles OS include Android, iPhone, Windows Mobile and Symbian. It is a must have for all mobile users!