  Wireless service providers track the time and location of all user
connections. Location inference attacks have been effective in revealing the
identity of anonymous users of wireless services. In this paper, we propose
ZipPhone, a solution that leverages existing cellular infrastructure to improve
user privacy. Spartacus allows a community of users to strategically time their
connections to remain anonymous while incurring a minimal loss of utility. We
evaluate ZipPhone from the perspective of a cell service provider and a
community of privacy-seeking users, and quantify the privacy/utility trade-off
of ZipPhone using two datasets containing cell tower logs of hundreds of users.
We present and assess a deanonymization algorithm that uses both location
profiling and trajectory linking. We find that by renewing identifiers every
ten minutes and remaining offline for 30 seconds, users can reduce their
identifiability by up to 45%.
