3 months after the festivals, we donated all unclaimed phones (who's owners we could not find) to charity.
TIPS/Suggestions to help in case you ever lose your phone:
Have your contact info visible behind the lock screen.
Have a very unique background photo
Have your full name associated with your itunes (iphones plugged into itunes say the name of who owns the phone).
If not locked, have your contact info in the phone (me, home, owner) something like that.
Check lost and found at the event you are attending before you leave. Sometimes when people find items they don't make it over to turn them in until after the concert themselves.