Out of around 200 countries in the world, only 75 have number portability. What explains the speed and pattern of diffusion of this regulatory issue? Research on policy diffusion offers several explanations: constructivist, coercion, competition, and learning. Constructivists argue that countries adopt a policy, sometimes even before they are ready, in order to appear modern and forward-looking. Coercive explanations argue that countries adopt policies because they are forced to through bilateral or multilateral agreements, for example. Competition explanations suggest that countries adopt policies in order to make them more comparatively attractive, to foreign investors, for example. Finally, the learning explanation suggests that governments’ beliefs about policies change over time. They learn when observing other countries implement a policy and monitoring its effectiveness. All of these explanations apply to diffusion of some policies internationally. The challenge is to understand which explanations apply more aptly under what kind of conditions and for what kinds of policies. To see which of these explanations applies to the global diffusion of number portability regulation, and through this single issue a view to the diffusion of communications regulation more broadly, first, I have collected data on number portability, the start of fixed line phone competition, and the start of mobile phone competition in countries around the world. This global data set, centered on three regulatory issues, provides some clues as to the pace and pattern of regulatory diffusion in the communications arena. Second, I have collected qualitative information on number portability discussions in five regional organizations – Asia-Pacific Economic Cooperation (APEC), Inter-American Telecommunications Commission under the Organization of American States (CITEL), European Union, Economic Community of West African States (ECOWAS), and Common Market for Eastern and Southern Africa (COMESA). These documents show which and when countries were interested in number portability. These qualitative data reveal patterns and links not evident in the global quantitative datasets.Finally, the paper concludes that examining regulatory diffusion through the lens of number portability suggests that Asia, Americas, and Europe are the three regions that innovate first; Middle East and Africa follow later on. Further, that in Asia and Americas, certain countries are pioneers, while others wait to see results before proceeding; learning appears to explain the diffusion pattern in these regions. In contrast , in Europe, regulatory diffusion begins early and proceeds rapidly, without the lag time observed in Asia and Americas, very likely because of the leadership and enforcement powers of the European Union, a coercive explanation among member states and a competitive one among non-member states. The data also make it possible to identify which countries often lead in regulatory innovation; conclusions that can be tested as more data on regulatory diffusion is collected for other communications issues. This is usable knowledge that can be applied to following the current diffusion of regulatory innovations across the world.