Start calling the people in the phones memory... you'll eventually get to someone who KNOWS that the owner lost it....

Happened to us... Herself left her stupid cellphone (I hate them all) in the back of a cab one day.... the cabbie found it and while he was away ato work the next day, his wife started calling people in the memory.... We started getting calls from our chums saying that someone had found our phone, so I called it.... she took my address and dropped it off about an hour later....