Jane wants to know if it's WhatApp or WhatsApp. Leo says there's an "S," so it's WhatsApp. A clever way of saying "what's up?"
Jane is thinking of getting her first smart phone so she can use WhatsApp to make phone calls. Leo says that WhatsApp identifies users by their phone numbers, not their names. So when people ask to use WhatsApp to make a call, that means they want not only their phone number, but also their contact list. Facebook is doing that to cross reference contacts with Facebook contacts, but you can opt out of it when you sign up.