When I turned sixteen, my sister bought me a new-fangled telephone. It had push buttons, but it was still just a rotary phone - when you pressed each button to dial, you still heard the rotary "tat-a-tat-tat-tat" with every number. I had held onto this phone ever since. It's cute. It works. There was no reason to get rid of it.
I was willing to bet that, in this day and age of advanced technology rendering yesterday's device obsolete on a daily basis, a telemarketer - who is likely going to be decades younger than my phone - would be unable to even identify a rotary phone by sight much less by sound.
And voila! Answering the phone with my rotary phone, and constantly pressing the buttons, the telemarketer kept repeating "Hello? Hello?" I then heard him turn to someone beside him and say "I don't know." He hung up... and immediately tried again. Once more, I answered with my rotary phone with the "tat-a-tat-tat-tat" over and over over the woman's voice calling out "Hello?" until she too hung up.
Time will tell, of course, but you may just be looking at:
The Telemarketer Killer!
You may laugh that I avoid technology under most circumstances. But every now and then a 28 year old piece of equipment will be the difference between you having your dinner interrupted, and me being able to sit down to eat in silence.