I still have one, and it works great. It worked so well, I had taken it out of the phone line, but put it back in a few months back when "Credit Services" began calling my house daily. I no longer get those calls and I'm leaving it inline now. BTW, TeleZapper is now sold on Amazon.Com
Wikipedia has a write-up of the TeleZapper, that includes a midi sound file. I suppose one could append that sound file to the beginning of a message on their answering machine, and save the cost of the TeleZapper. Something I’ll try myself. Wikipedia write-up says many telemarketers now bypass checks for those disconnect tones, but is effective for those that do check. Long ago a friend of mine used the long Rod Serling intro narrative from the Twilight Zone on his answering machine, and gave out a code to enter on the phone to bypass the long droning message. Doesn’t stop the ringing though.