In many Linux distributions the file /dev/modem is a symbolic link to the serial port containing a modem which is available for use.
Although the serial console is a serial port with a modem, we certainly don't want it used to place an outgoing call.
Check that /dev/modem does not point to the serial port being used for the console, say /dev/ttyS0. If it does, then remove the symbolic link.
Figure 7-3. Remove /dev/modem if it points to the serial console's port
bash$ ls -l /dev/modem lrwxrwxrwx 1 root root 10 Jan 01 00:00 /dev/modem -> /dev/ttyS0 bash# rm /dev/modem