This paper illuminates the workings of an informal industry in one of the poorest countries in the world. I study payphone operators in Rwanda using 427 million digital traces recorded on the mobile phone network. I demonstrate how to extract economic behavior from these traces. They reveal every call that generates revenue, as well as operators' critical business decisions: entry, the daily decision of where and when to work, and exit. Over the period I study, thousands of informal workers enter the industry. New entrants learn to optimize their operations within the first two months. Patterns are suggestive of business stealing.