Whatsapp is a easy to use application which can be used in any Android and windows phone as it requires less data and time to load is also less.
Not only about sending messages but more than that like pdf files, images, videos , docs to any whatsapp number worldwide.
Whatsapp ac is registered through a mobile number and a mobile data connection or a wifi connection is mandatory for using it.
We can also upload staus in it and we can chane our profile picture , any time we want .
There is no charge on using it, its completely free.