By now everyone has heard about Facebook’s huge $19 billion acquisition of WhatsApp with the addition of voice calls—but to some people that sounds a lot like Skype—leaving many to ask: what’s the difference? Facebook’s CEO, Mark Zuckerberg thinks WhatsApp will appeal to a younger demographic and change the game for Facebook’s mobile audience. In fact, Facebook’s recent acquisition of mobile devices like Instagram, according to this Reuters article, has…