Unless you’re the sort of person who keeps a lost iPhone you found in a bar — that’s still called stealing, by the way, and you might not get away with it — you can definitely try to return the device to the rightful owner with the Find My iPhone functionality. The process is quite easy, and you don’t even have to unlock the phone to do it, as Siri can provide a more than helpful hand.
As OS X Daily explains, all you have to do to find out the contact information of the iPhone’s owner is to hold the Home button of the phone to enable Siri’s voice search functionality and ask one of these questions: “Whose phone is this?” or “Who owns this iPhone?” Asking the question differently, such as “Whose iPhone is this?” might not provide the same results.
Siri should then display contact information for the person who misplaced the handset, including phone number, email and address, as long as it’s set up to run on the lock screen of the handset.
Naturally, older iPhones that do not have Siri support and thus can’t be returned using this particular trick. In such a case, you could always return the device to an Apple store, or wait for the owner to activate Lost Mode on the handset, at which point a message with contact information might be displayed on it.
An image showing how Siri answers one of the aforementioned questions follows below.