Telephone Directories for Mobile Phone Networks∗

Mobile phones have spread rapidly throughout developing countries, but they have done so without complementary information services (e.g., phone books) that allow users to search the mobile phone network. Communication costs have fallen dramatically; search costs much less so. We develop a search model that predicts both productive and distributive benefits from information services that facilitate search on the network of mobile phone users. We then describe a set of paired RCTs in central Tanzania, centered on the production and distribution of a paper telephone directory relevant to agricultural households. We randomized enterprises into the directory during a trial period, and randomized household access to the directory at the village level. The directory had substantial impacts on both sides, with large increases in the volume of calls to listed enterprises, and substantially greater use of mobile phones for business purposes by directory recipients. Using survey-based and incentivized measure of willingness-to-pay to be listed (for enterprises) or to receive a directory (for potential recipients,) we show that the directory exhibits typical characteristics of a public good.