Whatsapp's key to sucess was its most simple, and most multi platform design among all competitors. It worked on all phones ranging from S40 to the most modern OS, and it was the one who invented the concept of no username/account/manually adding contacts/password login..., but just a phone number and you're ready to go. Whatsapp has a very clean interface, ad free, also very efficient messaging delivery. You don't only compete on who's first, but who does it better. Apple hasn't been first in anything since the invention of the iPhone, but they are still successful in this domain.