While you are correct for the most part, I would point out that text services have wider distribution even if only for bandwidth reasons. But there are other reasons, there are good (enough) and widely distributed text standards (SMS), but not yet for video.

But maybe we are both over thinking it, does the old voice network reach even further?

Writing is reusable and presumably most of the learning going on behind rapid technological expansion requires literacy. Even just to navigate around Khan Academy.

Audio-only is a little better that way.

You can but it doesn't fundamentally change my points. The old analog audio network and the text systems have much larger reach.

Laying out enough digital network fabric to have skype and its kind everywhere is an admirable goal though.

Totally agree on this. I can video and audio chat with my grandma since apps like WeChat are designed for illiterate usage. Photos of participants, easy audio button, inline small videos.