This information was posted on the whatsapp official blog http://blog.whatsapp.com.
For more than a year, people have used WhatsApp Calling to talk
with friends and family around the world. It's a great way to stay
in touch, especially when connecting with people in other
countries, or when messages alone won't do. Today, more than
100 million voice calls are made every day on WhatsApp - that's
over 1,100 calls a second! We're humbled that so many people
have found this feature useful, and we're committed to making it
even better in the months to come.
Congrats to The Whatsapp team on this achievement.
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