There's a difference between finding and stealing, legally. If you find something abandoned, it's not your legal obligation to find the owner (I know I come from a family of lawyers).
If you come from a family of lawyers, then it is sad that you learned so little. If it is abandoned, it doesn't have an owner. "Abandoned" is the situation where someone didn't want an item anymore and left it intentionally so they wouldn't have anything to do with it anymore. This phone was _lost_, something completely different.
And yes, there is a difference between finding and stealing. Let's take California law, because most people should know more about it than you do because of the Gizmodo affair. When you _find_ an item, you have a choice: You can completely ignore it, or you can take it. Once you take it, you have the responsibility to return it to its rightful owner or to the police. And once it is clear that you are not going to do either, it is theft. That's what California law says.
In New York law, it is not called theft, but it is still a felony. In Germany, as an example, an item that is "lost" in a place like an airport, a bar, a train, is not legally lost because it is now in the possession of whoever runs the airport, the bar, or the train. So taking something from such a place is theft right there and then. If you find something on the street and keep it, that is again a different felony. And don't even think about picking up a lost iPhone somewhere in Saudi Arabia and not returning it.
Basically, any place you go has some kind of law that will make it some kind of felony to keep something that was lost.