Enable and disable ttyS0

I have a modem connect it to ttyS0 , in unix sco i know i can disable and enable the port , how can i do this , is there a command that will allow me to do this.
**** I'm running Redhat 9
*****External Usrobotics 56k

Thanks a lot guys

Try running the 'neat' command from the command line while logged in as root. You can enable and disable network devices through the GUI this program provides.