Since you mentioned elsewhere that you thought you saw a small telnetd implementation in an early BSD release, I went looking. The earliest BSD I could find that had a telnetd is 2.10BSD. 2.9BSD might have it, but I can't find the source for it easily, and 2.8BSD didn't have one. Anyway, the source is about 1200 lines of C and uses a lot of old sgttyb-type stuff that I'm pretty sure Linux no longer supports. It should be possible to port it, but I, honestly, don't really feel like it.

For anyone who's interested, here's a copy of the 2.10BSD source. 2.9BSD is there, as well, but it's not in an easy-to-get-at form. And here's a BSD Family Tree if anyone wants to try to find a different one. (IIRC, most of the 3/4.xBSD trunk was not freely available. Most of the changes in them were ported over to the 2.xBSD trunk, which were free. Then, starting with 4.3BSD, the free versions started being something else. The last free version was 4.4BSD Lite. But they all have enormous telnet servers anyway.)