In the 1980s, leading consultants were skeptical about cellular phones. McKinsey & Co. noted that the handsets were heavy, batteries didn’t last long, coverage was patchy, and the cost per minute was exorbitant. It predicted that in 20 years the total market size would be about 900,000 units and advised AT&T to pull out. McKinsey was wrong, of course. There were more than 100 million cellular phones in use 2000; there are billions now. Costs have fallen so far that even the poor, all over world, can afford cellular phones.