That is the number of of active users on the planet of SMS. It hold the distinction of being the largest data application with MMS closely following it up at 3.5 billion users. While white-hot unicorns like Whatsapp (who reached the 1 billion user milestone the other week) have been seen to be the largest data service in the world, the reality is that they hold a fraction of the 6.1 billion users of SMS. There is quite a bit of hype around unicorns and the ubiquity of their products but the reality is mobile phone users of the world are quite comfortable with this old-timey tool. We just need to catch up with them.