I used to get many telemarketing/scam calls. My phone is via cable and I use a Panasonic telephone that has a setting to disable the first ring. My computer does not have a voice modem, so I purchased one for $10. The software I use is called Phonetray Free and works great. After the first call, a number is blocked and then no more calls. Each call is in a log. The software also allows blocking of entire AREA CODES (like New York area, Miami, California, etc.). Only spoofed numbers can pass but since most spoofers are not too bright, they use the same number therefore no problem. My call volume has dropped by 99%. Phonetray Free has been replaced by Phonetray Pro from Softonic ($30). I have no personal stake in any of this.
When calling the number back (after *67) the phone is answered with "If you call from a cell phone press 1 if from a land line press 2. You press 1 and the next response is to enter your wireless number. No identification of who it is.