So I returned a preteen girl's cell phone tonight. This is the second cell phone I've found and returned. The first was lost by a mountain biking guy up on Santiago peak, it was just lying on the trail (I had driven up there with my son in my Subaru). It was charged and a little bit of snooping found his Dad. I left the phone in front of my house (not wanting to wait around to coordinate meeting), he left $20, which I gave to my son. He bought us all pizza with it one night.
This phone was trickier. I found it on a decorative pillar on the corner outside my house. It would only briefly power up. I measured the (3.7v nominal) battery at 2.87 volts (and got the polarity of the contacts that way too). Eventually, tonight I played around with powering it up from a Li-ion battery charger (4.2v) that I had, and wired the phone into the charger with some wires, no battery needed. It was a nice phone --Java, GPS, bluetooth, 1.3 MP camera, color screen, downloadable music, PacMan, Ms PacMan, Tetris, 16 MB internal RAM and quarter-Gig memory card, a Samsung with Sprint & web service. Service was disconnected though. But again, some snooping revealed the owner's landline and name (and friends, school, photos, fact that she has dances classes and braces, and texted once to a friend when her mom thought she was in bed at 10pm). Her dad came over and picked it up. I don't think he appreciated the research effort, though he might when she tries to turn it on and it doesn't work.
I still use a very basic monochrome Nokia 3310 with T-mobile prepaid and I have an address/landline sticker on the back. http://en.wikipedia.org/wiki/Nokia_3310 I got this around 2000-2001. Works for me.
