MikeSkyrme: As far as the recording and the 'prank' are concerned, I also believe it is illegal to record a conversation without advising the person receiving the call that they are indeed being recorded.
Depends on the law of the land. In this country a conversation can be recorded covertly if one party agrees to the recording. If the call had been made from NZ, the agreeing party (or parties) would have been the DJ's.
gzt: Someone would have to bring charges first. That isn't likely in this case. [Edit: my point about the radio station is they would not have expected the prank to succeed in this way. The radio station made the decision to broadcast the result and they have legal liability for the content of the broadcast obtained by deception]
A bit like above - depends on the law of the land. In this country "obtaining by deception" relates to obtaining ownership or possession of any property, or any privilege, service, pecuniary advantage, benefit, or valuable consideration, directly or indirectly. I can't be bothered hauling out my old deception module right now to get the accepted definitions, but I don't believe the tape recording would fall into any of them.