Nuisance calls
Most "robo" dialers wait until they hear something on the other end before they transfer a called number to a human.
That explains why you have to say hello 2 or 3 times before the other person speaks.
My SOP used to be- if I said hello and got no response within 2 seconds, I hung up.
That worked fairly well.
Now I'm just no bothered and don't wish to expend the energy so it all goes to VM unless I recognize the number.
I also tell people I prefer text like mentioned above, especially for a one time call.
There are a few states where robo-dialers are illegal.