When I was 9, me and my mate Megan stayed up late one night at her house and then decided to call one of those numbers that says something like "make new friends" whilst a girl dressed in her underwear plays coyly with the telephone wire and a guy in just his boxers giggles on the other line...
Megan pretended to be a Pamela Anderson lookalike (it was the 90's, after all) and we got some dodgy scouser called Dave who started perving down the phone at us. We left tons of messages with all these different people and then got bored and went to bed. Two weeks later, the phone bill arrived and funnily enough I wasn't allowed round Megan's house for quite some time...