[DECtalk] three DECtalk questions

[Mohamed]

Hi, so, I have three DECtalk questions that I'm wondering about. So, I 
know that with DECtalk, you can dial all all the standard phone numbers, 
and a, b, c, and d. The DECtalk PC only says about those, "for certain 
handsets only". So I'm wondering, what could a, b, c, and d have been 
used for? Also, what was the first version of DECtalk that was ported to 
software? I know the earliest speak window available is from 4.3, but 
I'm curious if there were software implementations before then. Last but 
not least, has anyone found the full, complete DECtalk PC documentation? 
Because it seems there are only 5 sections from the documentation, and 
I'm wondering if there are others.
Thanks.