A guy in Britain who was stuck on infinite hold with NTL, his cable company, figured out the menu-key-combo necessary to change the hold message. He put up a rude version:
"Hello, you are through to NTL customer services," they were told. "We don't give a fuck about you, basically, and we are not going to handle any of your complaints. Just fuck off and leave us alone. Get a life."
NTL sued him and lost, because the judges ruled that the message was merely "offensive" and not "grossly offensive" and so the haxx0r had not committed an offense under the Communications Act 2003.
Best line in the Guardian article: "NTL's media centre put the Guardian on hold, suggested we try another number and then declined to comment."
(Thanks, James!)