Hi, Bill! Save that fifty dollars! Cheap buzzard that I am, here's what I did: I went here and copied the SIT tone to my own hard disk (just in case this particular web page took it down at some later date and I needed it), then I placed my answering machine's microphone close to my computer's speaker and recorded the SIT as my answering machine's "greeting."
The recording has some background noise, but it's good enough.
Whenever the telemarketing calls become too much of a nuisance, I switch to the SIT greeting for a week or so. Then I go back to my regular greeting for a few months.
This works great on the "predictive diallers" and even on many human-initiated telemarketing calls.
You just have to make sure that there is a pause of 3 or 4 seconds between the end of the SIT and the beep telling your caller to leave a message (else you'll confuse the predictive software and may not get your number tagged as invalid). :-)
I usually have fun being rude to them, (asking them for their # so I can interupt THEM taking a dump), and my girlfriend gets mad at ME over it.