sudo launchctl remove com.apple.xserve.serial-ports
screen /dev/cu.serial <port_speed>
Replace the <port_speed> with the port speed supported by the device you are trying to control. This should allow you to connect to the device and control it.
When you are done, you can reset the Terminal by performing these key strokes
Type Ctrl-A and press Enter, then type Ctrl-\ and press Enter.