[lug] Repost: Can anyone give me a hand with pseudo-terminals?

[Bryan Field-Elliot]

I have an application which connects to a serial port... The default is
"/dev/ttyS0", but you can specify a different device on the
command-line. 
    
What I want to do, is point it to a pseudo-terminal. On the "other side"
of the pseudo-terminal, I want to attach a telnet daemon, or maybe just
one account via telnet, so that one can telnet into it and connect to
this application, which thinks its talking to a serial port. 
    
Obviously, only one person at a time should be allowed to telnet in this
way -- additional simultaneous attempts should tell the user "sorry,
port is busy, try later" or something like that. 
    
I don't know much about pseudo-terminals, they seem a little arcane to
me. Can anyone point me in the right direction as far as utilities I can
use, etc., or maybe just configuration tips? 
    
Thank you, 
    
Bryan