I have only a landline - I live so far out in the sticks cel coverage is poor, and I pretty much stay on my nature preserve anyway.
The huge fraction of robot calls wait for you to make a noise - it need not be hello, a fart will do, then there's a long pause usually and the salesperson will ask "am I speaking to $your name?".
If I haven't just hung up during that pause, which never happens with a real person...I have a number of things I will do depending on my mood. One is to immediately point out to the human that finally connects that not once in a long life has a machine-initiated (robot) call been for *my* benefit. Something along the lines of "how do you feel about that, click" usually happens then.
But wait, there's more! If I'm feeling more adventurous, I can often social engineer the person (females are easier) into telling me a name (if not an Indian...they are hip to this one), a place, and so on. I then point out that I now have enough info to turn their boss in for the felony they just committed as I'm on the do not call list. That will often stop them.
Then there are the Tom Mabe or the Henry Rollin's approaches - pretend to be the cop at a murder scene, or just an aggressively gay sex line (which these days probably doesn't work as well, but Henry makes it funny).
(don't play this loud over speakers at work - f bombs etc video is clean otherwise).
Then there's that outfit that uses some kind of annoying tape recordings to fool the callers, and sets you up to easily redirect to them - which I didn't find on a quick search because pranking or otherwise fooling with these robot callers is now quite "a thing".
OK, I usually don't have time, and they call at ideal times to be an interruption...but when I do, why not just have a little fun?