Have you ever run into an issue with over head paging and your IP based phone system?  Normally this is not an issue, if all else fails, you can always get an analog adapter and hook it up to your IP based phone system as another extension. The problem is when you have a hosted/hybrid type phone system like the PBXtra from Fonality.This is a problem because first Fonality will not want you to install a paging system, second they will charge you extra for a customer provided device requisition.Once you get over the first hurdle, the second option is real easy. We have successfully setup IP based paging systems from companies like Bogen. They offer a variety of systems even horns with built-in amplifiers. The most cost effective solution is to get one driver and multiple horns to cover the entire area and remember you can even have paging in remote offices/warehouses since you have an IP based phone system.