MWI on WPU-7700


I have a unitdata wp-7700. I’m trying to get it to display some form of notice that there is VM for the extension that it is registered to.

In the interface for the wp-7700 there is:

Use MWI y/n
Use Subscribe y/n
Subscribe Server:
VMS Alias:

I’ve tried every combo of these that I can think of, to no avail… Can anyone point me in the right direction? I can’t find any real documentation on it from Unidata…