General Info: http://wiki.ipitomy.com/wiki/Overhead_Paging

More General Info: http://www.voip-info.org/wiki/view/Asterisk+Paging+and+Intercom

Using an ATA (FXS): http://www.asteriskpbxsystems.com/asterisktopaging.html

FreePBX: http://wiki.freepbx.org/display/FOP/Using+an+SPA3102+FXO+Port+to+connect+with+Valcom+Paging+units

Viking PA-2A Manual

https://www.vikingelectronics.com/product-details.php?pid=317

http://www.grandstream.com/company/news/grandstream-networks-fxs/fxo-devices-certified-intercom-and-paging-systems-viking

1. Adjust the paging volume knob on the Viking PA-2A to a middle position (not off)
2. Connect an FXO port to the Viking PA-2A using screw terminals 5 & 6 (Trunk or Paging Port)
3. Set the DIP switches to 4 & 5 to ON (the rest off)

1. Use an FXO port on the Grandstream UCM610X PBX
2. Turn ON Talk Battery feature of paging amp
   • DIP switch 4 ON for Viking PA-2A
3. Create a new Analog Trunk named Paging
4. Create a new Outbound Route also named Paging
   • Set the Trunk to Paging
   • Set the Dial Pattern to 999
   • Strip the digits used to access the trunk or you will hear the dialed tones when paging

Evidently, on the Grandstream PBX, you can not strip all the digits as the PBX won't let you enter 3 to strip out the tones for 999.