1. Install socat

$ brew install socat

2. Create a pair of virtual serial ports

$ socat -d -d pty,raw,echo=0 pty,raw,echo=0
2011/08/25 21:31:10 socat[57798] N PTY is /dev/ttys005
2011/08/25 21:31:10 socat[57798] N PTY is /dev/ttys006
2011/08/25 21:31:10 socat[57798] N starting data transfer loop with FDs [3,3] and [5,5]

3. Communicate between ports using in.py (reads from port) and out.py (writes to port)