Each message sent or call made is absolutely free.
With WhatsApp, you can send messages or call other users without worrying about character limit or the number of messages sent. So when WhatsApp came out that same year, it became the new and convenient way to do the former.
In 2009, software that offered free calls and messages could be found mostly on desktops, not smartphones. With 1 billion active users, Whatsapp will connect you with the people that matter to you the most, both near and far.