We installed one of the Nitsuko voice bricks on a DS2000 back in around the year 2000. Customer called complaining some callers were cut off. Came to find out Nitsuko was using dial tone as the disconnect order for the voicemail. So some men with deep voices would be leaving a message if they stopped and stuttered with and ahhh the system would disconnect.
Once this was figured out I could make it disconnect every time by saying and ahhhh.

Nitsuko had no fix at the time so we pulled it and installed a Voicegate Wizard. (also used the brick)

We get old too soon, smart too late