The "RoboKiller" Android app will automatically answer known spam calls on your phone with "Hello" in a random voice then waits for the callers agent to come on and greets them with some random phrase followed by other random phrases saying you can't make out what they are saying etc.. It records the callers reaction for your later amusement if you choose to listen to it. I used to use it but got tired of paying $25 a year for it.
If a spam call does get through to me I am interested in their scam but I have a caller on the other line so please hang on for a bit. Some of them will hang on for several minutes. Some even call back later at which time I very politely also happen to have a call on the other line...