Once I identify a spammer, I add them to a forward. I have a voicemail account and have uploaded an audio file grabbed from a telephone archive site. The audio starts out with a SIT tone, then the following message...
"Due to the earthquake in the area you are calling, we are unable to complete your call as dialed"... it goes on but you can see the humor.
When I was running an Asterisk server, I sent telemarketers into a queue where no one would ever answer. They heard the "Your call is very important to us... and You are Caller number 1 in the queue". Then Instead of music, I played commercials for a product I sell, over and over and over and over and over. :-)