Like if you are interested in the convo then you should be paying the other person as you are getting value from the convo.
What's the situation where you don't care about the convo but for the right price you could care, and the other party also thinks that price is reasonable? Like maybe if someone is trying to recruit you i guess, but the situations where that is true seem very few and far between (and we already have a system for that, where traditionally someone offers to buy you a meal in exchange for listening)
Like if you assume a CPM of $2, that means $0.002 per phone call. Would you really find that acceptable?
If the answer is no, then you aren't really accepting payment,you are just blocking people with extra steps. No different than if you said you will accept a phone call for a billion dollars. You aren't really accepting something for payment if you set a price that nobody will pay.