What's the use of the RJ-11 connector at the front of the desk?

I have worked on a wholehog III console a lot, but now i have one with a RJ-11 (?) connector at the front of the desk under the armrest.
Never seen that before. What's the use of it?

I searched the manual and this forum but can't find any information about it.

www.rdirkmaat.nl/images/stories/hog3rj11s.jpg
Related