Comment by kragen

The old LPC-10 codec isn't quite as frugal with bits as gzipped ASCII, but it still only requires 2400 bits per second of message, around 800 bits per word instead of 3. Codec2 is a little tighter still. If you're store-and-forwarding those bits over a low-bit-rate radio relay network, say 25 bits per second, a 24-word message might take 12 minutes per hop to send, plus whatever the latency is that you wait for the relays to start listening. So I think it's pretty reasonable to have a model where you dial a phone number, it reads out the name of the person who has that phone number, and then you hold down a button to record your message.

The more difficult problem there is infosec, I'm guessing.

But we shouldn't exaggerate the literacy problem. This is Argentina we're talking about, not Lesotho or rural Laos; Chubut Province had 98% adult literacy in 02010, and that's probably improved since then, since everybody uses WhatsApp now.