WhatsApp is starting it's own mobile service provider business, that's what's happening. It's pretty normal that - just like roaming charges - extra charges for WhatsApp, which is becoming a VOIP service, would be billed to the users.
It starts in Germany, where they have reached a deal with Telefonica's E-plus network, which is becoming the WhatsApp/Facebook carrier.
It's Zuckerberg's turn to get his arse whipped by the EU Commission. When will those cowboys ever learn...