Whatsapp delivers 10 billion messages a day

"Last October, BGR broke the news that WhatsApp was delivering 1 billion messages each day. This caused quite a stir, as it dovetailed with some mobile operator warnings about declining SMS volumes, most notably by KPN. On Thursday, just 10 months later, WhatsApp confirmed that it is now handling 10 billion messages a day — 4 billion inbound messages and 6 billion outbound. How’s that for a hockey stick? The disparity between incoming messages and outgoing messages highlights the popularity of the group messaging feature, which plays a big role in the app’s success."
Source:  Yahoo/BGR, 23rd August 2012
Earlier - 1 billion messages a day (Sent only)