FBarix IP Audio devices are ideal products to extend a SIP based phone system (PBX) such as Cisco Callmanager, Asterisk or OpenSER with paging functionalities.
All Barix Exstreamer and Annuncicom devices can be loaded with the SIP firmware (which is a free download from the website). Once this firmware is loaded, the devices provide a functionality similar to a specialized phone.
For paging applications, an Exstreamer (output only) device suffices.
The device can be programmed to auto-answer an incoming phone call, activate a relay with call reception (to activate a paging amplifier, for example), and output the call audio received through its analog output. Depending on the device, you have a choice of line level, 600Ohm balanced or even 2W, 8W or 2x25W amplified output, suitable to directly drive overhead speakers. Some device models (Exstreamer 110/120/500, Annuncicom 100,200,1000) provide at least one contact closure output (relay).
These contact closure outputs (up to 8 with the Annuncicom 1000) can be used for zone control, assuming that the SIP Paging gateway (Barix device with SIP firmware loaded) is connected to a traditional paging amplifier, which has inputs with which zones can be selected. Details on how (as an example) an Asterisk PBX is configured to drive the Zone Control relays on an Annuncicom 1000 are in this wiki article: Asterix_Server_configuration_for_Relay_control
Other PBX systems should work similar, and you can always control the relays even in-call by issuing certain commands to the device (common speak, you would say via DTMF, technically, button presses are typically delivered using SIP INfo or RFC 2833 encapsulation). Details are, again, in the article referred to above.
So .. Barix devices are ideal SIP Paging and Intercom devices, useable in a vast range of applications.