--- - |2 Mobile devices have spread throughout the developing world at a rate unparalleled by other communications technologies. Yet surprisingly, little is known about their impact on social networks. This study analyzes three waves of pooled survey data in Nairobi (2002, 2007, 2013). We focus on the size, composition, and location of important personal relationships—that is, “core networks.” Networks of close ties have nearly doubled for urban Kenyans, as network composition shifted toward kin and away from friends. Indeed, friendship decreased from over one‐third to less than a fourth of close ties, while family ties grew from one‐third to nearly half. The geographic distribution of networks has become broader, moving away from local ties and toward national (but not international) relationships. Finally, the pace of change declined as mobile devices became embedded in daily life. - 'Sociological Forum, EarlyView. '