My point was that they're already deploying counter measures. They also tend to use a two tier system where the first person you talk to is an idiot who reads lines. If you bite, they second you to a second tier to close. If you're not a real person, they hang quickly at the first tier. I've gotten to the second tier and really pissed someone off (mission accomplished) insisting that I was the old lady they were calling, when I clearly had a man's voice.
I use to use Google's call screening, and was foiled by this when I wanted to screw around with them by pressing buttons to speak canned messages. Google really needs to update that with a DTMF keypad.