I've found 5 cellphones, mostly walking the dog... The two that were functional, I returned to the owners, the other three I parted out. Two SD memory cards, two batteries, one small LCD (no specs, probably no use), three vibrating motors, small speakers, microphones, a camera element (no specs either), tiny LEDs... I play with electronics, so can make use of some of the parts.
Should try and return them, if you can, it's like finding a wallet, there is usually something in there worth more to the individual, that the replacement cost...