I'm sure I'm not the first one to think of this, so I'm wondering "why not?"
Wouldn't it be nice if computer terminals could be placed in airports and shopping malls so you could just plunk in a quarter and send an email? It would be just like a pay phone, but with some obvious advantages.
You could type in "Delayed in Chicago. Pick me up LAX at 7:00 pm."
Try that with a phone and you could make contact with a person or an answering machine or maybe just a busy signal. Email almost always gets through and it's cheaper.
I doubt that a computer with a coin slot and no frills would cost much more than a pay phone. It wouldn't even need two-way capability, or memory to store messages. A simple monochrone monitor would be okay. It would be quicker and cheaper than a long distance call and hearing impaired people would love it. If you had to have an extended discussion, you could still use the phone.
Howard