Long before we ever heard of Mel Greig and Michael Christian or Jacintha Saldanha's suicide, there was another Royal Prank. The Original Royal Prank was committed by Canadian DJ Pierre Brassard in 1995 (which proves that there's nothing about pranks that means they will all end in suicide), but that time the queen herself was the target.
In 1995, Brassard called the queen pretending to be Canadian Prime Minister Jean Chretien. He was put through and talked to the queen for 15 minutes and was able to get her to promise to try to influence Quebec's referendum on independence proposals.
That's a much more significant joke than what Mel Greig and Michael Christian were going for. Pranks have always been a part of a radio (including Orson Welles' famed War of the Worlds broadcast) and always will be.