When I was getting my first modem, I was very seriously thinking about building it myself. In the end, I decided to go out and spend the $800 it cost to buy myself a 300 baud modem. It was agonisingy slow, but at the time.......
A little later I got into Viatel, and purchased a second modem specially for it, which ran at the blistering speed of 1200/75 baud. The two were totally separate, so they were connected together with a switch.
Incidentally, in those days, the modems did not have dialling facilities, so a telephone had to be connected with it as well, complete with ancient rotary dial, so that I could dial up the BBS.
I still have a 1975 300 baud rack mounted modem card somewhere....
