We are trying to create an IP based PA system for my institution. Our first hunch is to use an asterisk server with clients in auto-answer mode. Is there any better method, or a more apt open source framework? Our internal network is fiber backboned with mostly *nix systems.
You might want to start looking at an RWALL command as a framework and instead of text send audio files.
Conversely you can have a very simple multicast server and client that does exactly the same thing.
Security would be your biggest concern since both approaches are inherently insecure.