I am not a WhatsApp user but a number of my friends use it. I think what they did well are: (1) You automatically upload your contact list to their servers. If

I am not a WhatsApp user but a number of my friends use it. I think what they did well are: (1) You automatically upload your contact list to their servers. If any of friends start to use WhatsApp you will see it on the list (2) Smart phones were gaining adoption in many Asian markets and their value proposition of cheap unlimited messaging plan resonated very well (3) They charged for their product after initial adoption so they don't have to be tied to VC money forever and avoided annoying users with ads.