Connection to overhead paging

[jcoole]

Hi all,
I'm still relatively new to being the phone admin and I cannot figure this out.
Using CM 5.2
We have an overhead paging system that is connected (somehow) to the endpoints.
A user can dial 85, wait for a tone, then 00, and they are now on the overhead system and can announce campus-wide. We plan to upgrade later this year, and I want to be sure I understand how this works, lest it breaks.
I do not see 85 as a feature access code, so my question is this:
What dark magic allows this to happen?

[marzahn]

Overhead paging commands . . .

display dialplan analysis
change paging loudspeaker

[jcoole]

We use a TOA 900 series amp with a variety of generic speakers.