The Stern staff have been guilty of fake prank calls in the past. I couldn't find one in the link you provided, but I listen on Sirius and hear them occasionally. The most obvious one is a call to an Asian clock repair business where the owner is supposedly mispronouncing the word "clock" as "cock". Not only is that NOT the way Chingrish works (it would be "crock" if anything) but the way she goes out of her way to talk about how big the cock is and how old, etc is obviously fake.