Sometime in the mid 1990's a new set of telephone services were launched in Australia. Along with the usual suspects such as phone sex, dating and sports scores there was a number you could call to 'The Deaf Man'. 'The Deaf Man' was not a number you'd ever call yourself!
These new services were initially launched as 0055 numbers and, as such, they didn't look a lot different to an interstate phone number. I think they've become 1-800 numbers these days but I'm not sure; if so that's a good thing because it's instantly apparent that it's 'special'.
We used the initial similarity of the number to a 'real' number to good advantage. We'd pick a suitable victim at the office and leave a 'while you were out' note on his desk requesting that he call the number.
Such a conversation would typically go something like this:
Victim: 'Hello, this is so and so returning your call.'
Deaf Man: 'Can you speak up?'
Victim: (A little louder) 'Hello, this is so and so returning your call.'
Deaf Man: 'I'm sorry, I can't hear you'.
And so on. The longer the call went the more The Deaf Man implored the victim to speak up or more clearly or repeat that or... And the longer the call went on the louder and more frustrated the victim became!
Yeah, I was 'got'! How else would I even know about it? Most people in our office were 'got' at one point or another. One woman, not the brightest penny in the purse, was 'got' about 5 times before she understood the joke!