Over the last two decades, cellphones have ushered in a communications revolution in Africa. The entire country of Mali, for example, has just 120,000 landlines to serve a population of 15 million. But as of 2012 there were enough cellphones in service in Mali for every man, woman and child. The spread of cellphones in this way has driven innovation across the continent. M-Pesa, a text-message-based money-transfer system, has made financial services available for the first time to millions. Another enterprise tells rural farmers by text what their crops might sell for in distant markets; mass-texting campaigns have helped promote major public health initiatives.