Secret Service confiscates cell phones of tourists near Obama WTKK radio | 8/24/09
Posted on Mon Aug 24 16:10:09 2009 by pabianice
I think there one more instance, in addition to the one at the burger joint you mentioned. I think the SS confiscated cell phones at a restaurant (a nice restaurant) either in DC, or during Barry's date-night to NYC a while back.
It seems to be a pattern of behavior.