I like all of these suggestions, but if you decide no, you want something else, an idea struck me. So, instead of them appearing behind the group, of the person call someone and then when they hang up, the person goes on a rant about whoever was on the phone, just to find out the call has not ended. I did that once with my mother. Someone from her work had called her and she put on her fake, nice voice, then right when the call ended she began cursing the chick out. So me, being a comedian, said, "Mom, you're still on the phone." And my mom freaked out. Funniest thing ever, it was great.