  We report a user study of over four months on the non-voice usage of mobile
phones by teens from an underserved urban community in the USA where a
community-wide, open-access Wi-Fi network exists. We instrumented the phones to
record quantitative information regarding their usage and location in a
privacy-respecting manner. We conducted focus group meetings and interviewed
participants regularly for qualitative data. We present our findings on what
applications our participants used and how their usage changed over time. The
findings highlight the challenges to evaluating the usability of mobile systems
and the value of long-term methodologies. Based on our findings, we analyze the
unique values of mobile phones, as a platform technology. Our study shows that
the usage is highly mobile, location-dependent, and serves multiple social
purposes for the participants. Furthermore, we present concrete findings on how
to perform and analyze similar user studies on mobile phones, including four
contributing factors to usage evolution, and provide guidelines for their
design and evaluation.
