It's cool that we can build something ad-hoc, and then basically take that idea to CN and copy-paste it a thousand times for a cheaper, more reliable product.
For example, here's this idea for VoIP intercom / paging. We can buy it for $$$ from Cyberdata or we can source it directly ourselves.
If you decide to test Snom, set the parameter Identity 1 - SIP - Auto Answer to ON. This will force the unit auto-answer immediately after being called... by connecting amplifier to the headset output of Snom300, we have fully functional floor paging system for under $100.