From No Telephone to Smart Phones 1900-2011
In 1982, there were 4.6 billion people in the world, and not a single mobile-phone subscriber. Today, there are seven billion people in the world—and six billion mobile cellular-phone subscriptions. As with many technologies, the explosion began in the world’s most developed countries.
From: http://www.technologyreview.com/business/40321/?nlid=nldly&nld=2012-05-10
h/t +John Verdon