The flip phone!
Let me start off by saying I enjoyed this film on the first go around.
I just watched it again, and as someone mentioned,it's definitely one of those movies you have to watch more than once. I enjoyed the nuances missed on the first pass such as Shirley Maclaine and Sean Penn's small gestures and reactions, and really enjoyed the soundtrack and cinematography.
Oh and flow of the movie hiccuped for me each time that flip phone was used in the boonies. But over all, it was a well spent 2 hours!