There are three possible methods to integrate overhead paging to the PBX; SIP, FXS, or FXO.
Using a SIP based overhead paging device is the best option as the device registers directly to the PBX as a SIP extension. This allows for the easiest integration as we do not need a gateway between the PBX and the paging device. In order to page, you will dial the SIP extension, and since it is registered as a SIP extension, you are also able to add the overhead to a paging ring group, along with the other extensions on the system.
An FXS paging device requires an FXS gateway (IPr20, PAP2, Granstream, or SPA112) to integrate as a SIP extension and is the second best option. Again, you would dial the extension to page, or you can add the extension to a ring group and page overhead along with a group of phones.
An FXO paging device requires an FXO gateway (IP400 or Grandstream) to integrate to the PBX. Using an FXO paging device is the least advised method for a few reasons. The main reason is how you make the call. Instead of registering as an extension that can easily be dialed, you have to create an Outbound Route to access the