You can check if the modems or other ACUs are not working properly in several ways.
Get counts and reasons for contact failure by running:
uustat -q |
Call over a particular line and print debugging information on the attempt.
The line must be defined as direct in the /etc/uucp/Devices file. (You must add a telephone number to the end of the command line if the line is connected to an autodialer or the device must be set up as direct.) Type:
cu -d -lline |
where line is /dev/cua/a.