Cell phones have become an integral part of our lives.  They allow us to keep in touch, access the web, and use a variety of apps and games virtually anywhere.  They can also play a big part in both civil and criminal cases.  Cell phone towers can triangulate a signal, allowing GPS tracking of the phone's position.  Likewise, call details, text details and content, IP information, billing info, and even store surveillance cameras can be accessed through subpoena to prove various facts at trial.  Below is information obtained by open record requests by the American Civil Liberties Union that displays how long certain cell phone companies retain this information:

https://www.aclu.org/cell-phone-location-tracking-request-response-cell-phone-company-data-retention-chart

Keep up with ACLU's efforts to protect your cell phone privacy:

https://www.aclu.org/protecting-civil-liberties-digital-age/cell-phone-location-tracking-public-records-request