It is loud speaker paging. You dial the analog extension and will hear dial tone back or a couple beeps, I cant remember. Then dial the code for the announcement you want to hear and hang up. Your connection to the device is live because you called an exetnsion, but it uses audio out line level to interface with your PA amp. I think it can hold 4 or 5 pre-recorded messages. You record them in your voice by calling into the device and accessing the admin menu. It also has different sirens and tones you can use. The manual on the website has all the instructions on how to set it up and what it can do.