Well, don't keep it a secret. Do they have a web site?
here is where you'll find it...
Sorry, I guess I thought it was more well known than it was. Just learning it myself, though our other Tech has been servicing the Super Key (now discontinued) for some time.
We also just installed a new phone just last summer.
It's the TDS 600 Hotel/Motel Feature Package.
It's a pretty robust system, though we had to update it at one point.