Well there's already speech-oriented codecs that can go down below a kilobyte per second, and there's this one that throws a neural net at the problem to help squeeze bytes: https://ai.googleblog.com/2021/08/soundstream-end-to-end-neu...

I don't think I've ever had a functional connection slower than that. You need packets to be making it through in a timely manner if you want a voice conversation, after all.