WhatsApp - A free application that can be downloaded by any one on any phone. It is a messaging application that gave BBM(Blackberry) a very tough competition. Although BBM was considered as the best messaging software, whatsapp soon took over and was indeed better in every way possible.
One major difference between the two was the number of emoticons one can use on Whatsapp. I persinally use whatsapp on a major scale which also helps me to stay connected to people all over the world.