This document outlines a mobile data visualization hackathon called "A Day in the Life of a Smartphone". The goal is to help marketers understand mobile usage by visualizing how people interact with their phones. Teams will use anonymized mobile data sets to create interactive visualizations, which will be judged on understanding, originality, style, and presentation. The top 10 teams will present their visualizations for prizes. The hackathon runs over two days, with data sets and guidelines provided for participants to analyze mobile clickstreams, profiles, and usage patterns.