Australian radio DJs don't have great form when it comes to prank calls, but fair play, this one is actually really funny.
Hamish and Andy worked out that using their office phone system, they could connect two separate lines on a conference call without having to speak themselves. Obviously the only logical way to use this technology is to ring two phone sex lines and have the girls chat to each other without knowing what's going on. The result becomes some kind of weird verbal sex tennis.
Skip to around 1:50 to jump straight in at the good bit.