Special Information Tone (SIT)

Ok, so this falls in to the category of obscure – but useful. An acquintance of mine was telling me the other day how he reduces the number of phone solicitations they receive.
There is a tone the phone company plays over the receiver when you dial an invalid number. He has recorded that tone and put it on his answering machine. It plays, there is a pause and then he greets the caller like you would normally.
The automated dialers these marketing firms use listen to the response. If they hear the phone company’s ‘invalid phone number’ tone, they don’t call back and they don’t put your number on a list for resale. So that’s a good thing, right?
He passed along the web site where the Special Information Tone (SIT) for an invalid phone number tag can be downloaded. I’m going to try it on our phone.