Lots of good input but I'm still not sure what I would do if I had to change my current system. I think my best option is to step back and review my requirements and see what fits rather than looking at different products and try to see how they could be made to work. I don't think one product is going to cover everything.
These are my MUST HAVE requirements:
Paging-
Simple whole house announcements from anywhere in the house to everywhere in the house. Must mute any music playing to enable the announcement to be heard.
Intercom-
Don't really use room to room conversations much but do need to drop in and monitor areas sometimes. Door intercom is probably only instance where 2 way conversation is needed.
Announcements-
Don't care if this happens via Paging System, Whole House Music System, or Phone System but must have announcements for incoming caller ID, vehicle in driveway, which doorbell is activated, mail delivery, motion in garage, etc. These announcements need to mute any music playing to ensure they are heard.
Phone-
Must support multiple lines and provide speakerphones at all locations
Must have indication when phone lines are in use and at least one display in some location to monitor when extensions are left off hook.
Must have some kind of voicemail with an indicator at all locations when there are messages waiting
Must have a way to interface to other systems. Must automatically mute music in the room where a phone is in use (and only in that room. Muting must not affect music in other rooms)
Must support at least 24 phones in fixed locations. Do not want anything that can wander and not be where it is needed. Do not want anything that needs to be charged or can otherwise get into a state where it is not instantly available for use in an emergency.