A Brooklyn teenager became a cyber-sleuth when she used the MySpace Web site to track down a teen who mugged her on the street and stole her cell phone... But the thief underestimated a tiny piece of modern-day technology found in many cell phones today: the SIM card, which contains data unique to only the individual who owns the phone, including phone numbers, e-mail addresses, etc... After the robbery, the mugger checked his own email using Polanco's SIM card. So when Polanco, a junior at Norman Thomas High School, had her old information transferred to her new phone, the mugger's e-mail address showed up...