tions (number years to reach 80% coverage) 5 One of the reasons mobile phone technology has spread quickly is that it has followed other technologies that may have eased the way. Figure 2 confirms this sequencing property is likely at work, at least in the US: many of the new technologies that were introduced before about 1950 (with the exception of radio) were relatively slow to diffuse through the population, whereas those introduced in the second half of the century saw generally steeper adoption rates. Nonetheless, the speed of adoption of cell‐phones, especially in the developing world, remains unprecedented. Figure 2: Technology adoption is getting faster 6 5 Data from World Bank. 6 Source: New York Times, February 10, 2008. 0 20 40 60 80 100 120 140 Railw