He found it. He took it. Now wait... he didn't make any serious attempts to return it to the rightful owner but instead kept it. That's what makes it theft. According to Californian law, and just check the site below - it's theft in the UK as well.
http://news.bbc.co.uk/1/hi/magazine/8129534.stm
Amazingly you still don't get what I'm saying. It's only theft if you attempt to profit from the find in which case it's fraud. Finding the item is not a crime but pretending to be the owner in order to sell it or in this case claim a prize is fraud or misrepresentation. If they'd just thrown the ticket in the bin they would not be committing a crime.
That's why I suggested that what this guy should have done was take a load of pics of the iPhone 4 he found and then send it back to Apple or hand it over to the police.
He could then make money selling the pics without committing any crime.
PS If you read this guys story he states that he did phone Apple to report the find but they were not interested. If you attempt to return something and the owner doesn't want it then I'm fairly surely you can legally keep it.