Whatsapp is a good messaging service now owned by facebook.the users are reaching billion mark as the ui was simple and real time messaging is there.whatsapp is now a major part pf social media and connects the people in a better way.you can share images , songs and pdf documents as well.
There are also other messaging services but somehow whatsapp is able to be on the top.earlier it is paid after one year of free service but now it is free for lifetime so that users can enjoy there free messaging as long as they are willing to.good and awsome app.