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Facebook notes that WhatsApp has over 450 million MAUs, with 70 percent of those active each day. In a staggering comparison, Facebook also notes that the messaging volume of WhatsApp approaches the SMS volume of the entire global telecom industry — and that it’s adding 1 million users a day.

From TechCrunch piece on FB buying Whatsapp 

It is astounding that a single messaging app could rival the volume of the entire global SMS industry.