I'm not so much looking for "modem control" as much as I am
creating a "tunnel" or "pipe" (not sure of the correct noun)
of a serial port on one box on the network, to a virtual com
port on another. While one use would be a modem I actually have
a number of serial devices I'd like to control if I could get
it to work.

At my place of employment we use serial "hubs" to IP to
embedded linux hosts which works slick, but that's a spendy
solution for a hobby setup at home. Digi I/O makes them I
think, as well as Black Box.