Does it has a serial cable plugged into the SMDI port on the front of the voicemail?
The serial cable goes from the BSIS card to the SMDI port on the Tis16 VM.
The other way is to chech the configuration in P578 and P579 VM settings in the CTX28

The I/O programming for SMDI will also be set for Serial port 1 with 1200,7,E


Regards
Carl