I found one on the beach one time. No lock. I picked a random number from the contacts list and called it. It was a funny/strange conversation at first. "Hi, ah, this is going to sound crazy but do you have caller ID? Do you know who this is calling you? I found this phone and ..." Turned out it was the young lady's uncle I had called. We managed to contact someone else with her and met her in about 20 minutes at a ranger station just down the beach.
I figure I either made her day - getting her the phone back...or I ruined her day when she was hoping to justify getting a new phone having lost hers... ;-)