On April 1, 2008 a New Zealand radio station (The Rock FM) promised an intimate performance by Foo Fighters but the fake concert brought an overwhelming amount of inquiries and the station would up apologizing.
On April 1, 2004 Portland pet owners were fooled by a story on the air which said they would be fined if their furry friends weren't buckled in seat belts
On April 1, 2003 a Cleveland, Ohio deejay made his audience believe he had tethered a cat to helium balloons and it was flying out of control.
On April 1, 2002, a deejay from South Africa told his audience that the President of the country had been shot dead in Zimbabwe.
There have been plenty more and I've documented many on this site.
For more examples of radio's twisted sense of pranking, check these articles out: