To all the cynics out there...
Last year I left an iPhone AND a wallet on a bus from La Plata to Capital. The wallet had over $150 US cash and credit cards, the iPhone was unlocked and almost brand new. I left for Canada the day after this happened - but used the find my iphone feature to lock the phone and leave a local argentine contact number of a friend on the screen of the phone. My friend received a call the next day, an older lady had found the phone and wallet, but was reluctant to return it to someone who wasn't the actual owner. She actually contacted me via Skype, where she verified it was indeed me, and I asked her to please give the phone and wallet to my friend in Capital. She gladly obliged and met my friend, who brought along a box of alfajores for her troubles and ended up having a coffee with the lady who happened to be a retired school teacher.
True story.