Live on stage at Nokia World 2013, WhatsApp CEO Jan Koum announced the instant messaging service now has 350 million monthly active users. That's up by 50 million since August, when the network announced it had hit 300 million. Koum also announced that some 250,000 users per day are registering for WhatsApp using Nokia devices — including Symbian, Asha, and Lumia handsets — over 7 million per month.