Lucent voicemail box - keyboard input mystery

[deskman]

Adrian's Digital Basement trash picked a 20 year old voice mail box from Lucent. The box basically is an old 386 system with a few telecom boards.

He is having trouble connecting a keyboard and has tried a few routes.
Lucent Merlin Mail, Release 3, MM04, ~2000 production.

Real keyboard action starts at about 17:00 but the whole video is worth watching. This guy doesn't give up!

https://youtu.be/gcUc4e0Q7ak