We’re entering a new stage—call it the post-iPhone era. Cheap. Smart. Ubiquitous. Profits then flow to the best services that utilize smartphones. Facebook FB +4.52% is cleaning up with its mobile-ad sales. Twitter, TWTR +5.90% Snapchat and Instagram are all driven by smartphones. Uber and hundreds of new apps wouldn’t exist without smartphones. It makes sense that Apple is interested in acquiring Beats Audio for a reported $3.2 billion. And all this is at a billion smartphones. What happens at three billion devices? Or four billion?

First, dirt-cheap smartphones will have astonishing implications for the global economy: Smartphones are a productivity platform for wealth creation. Americans may waste days playing Piano Tiles or Clash of Clans, but the developing world can build lives with a $35 smartphone. Roughly 20% of the world population earns less than $2 a day, and the cost of a smartphone just dropped from a year’s earnings to three weeks’ pay. Now that’s an antipoverty program.