IPhones store lots of personal data.

IPhones store more information than users may realize, and some of it could be used against them if they're ever charged with a crime.
Law enforcement officials have long used phone records and, more recently, e-mails and text messages to help solve crimes. Now a field of forensic study is emerging that deals with iPhones specifically, targeting GPS data, browser history and other potentially incriminating information.

"Very, very few people have any idea how to actually remove data from their phone," says Sam Brothers, a cellphone forensic researcher with the U.S. Customs and Border Protection who teaches investigators how to retrieve IPhone data.

Self-described former hacker Jonathan Zdziarski, who has written a book, IPhone Forensics, has been tapped by agencies nationwide to teach how the information is stored.

Links:http://viaforensics.com/wpinstall/wp-content/uploads/2009/03/iPhone-Forensics-2009.pdf
http://www.usatoday.com/tech/wireless/phones/2010-07-07-iPhone-forensics_N.htm