Vgetty must be properly installed and working with your modem before configuration will yield positive results... please see the Vgetty installation page if you haven't already done so.
Now that you have vgetty up and recognizing your modem, we need to configure it so it will use VOCP as the program which deals with incoming calls. There are only two or three lines to modify.
As root, backup and edit the voice.conf file (probably in /etc/mgetty+sendfax/). Find the line that starts with
and set it so that it points to your modem:
replacing X with the appropriate number (if you are from the windows world, remember that ttyS0 is COM1, 1 is COM2 etc). If vgetty was already working, you can just leave it as is.
Find the line with:
and set it to:
or wherever your perl executable is installed.
Now find the line with:
and change it to:
Also set the line with answer_mode to:
You may also want to tweak: rings, rec_max_len, rec_silence_len, maybe some others. Read the comments within the file itself - it is rather well documented.
Finally, if you've applied the VOCP patch to mgetty, you can use the new force_detect option in the voice.conf file. This will forgo vgetty's normal autodetection and force detection as a particular modem - this may or may not work with your modem, obviously. Add a line like:
changing PORT to the ttySX where your modem resides and setting MODEMTYPE to one of the types specified in the output of `pvftormd -L` (eg US_Robotics, Elsa, etc.)
We recommend you start with the default values that are in voice.conf and change them if necessary.