Obviously I don't mean last week's call by 2DayFM DJ's Mel Greig and Michael Christian, which ended in tragedy

For me, the genre works best (and occupies a higher moral ground) when the victim is an authority figure, or at least makes some claim to authority, as in the example below of a prank call to a TV psychic.

That caller - Robin Cooper - is the alter ego of British comedian Robert Popper, who as well as his involvement in hit shows such as Peep Show and The Inbetweeners, is a seriously talented wind-up merchant. More Robin Cooper prank calls here.

Given their high humour potential, it's perhaps surprising that prank calls aren't used more often for advertising purposes. Probably something to do with the difficulty of getting clients to sign-off an unscripted script. 

But here's one fine example, for McDonald's, from 2009.
This campaign, for Apple Tango, dates from 1995, and it takes the biscuit. If you haven't heard it, you're in for a treat.

After last week's events, I doubt we'll be seeing too many prank call-based ad campaigns in the near future. Which is a shame really, because when they come off, it's a very disarming technique.