The way we did it was to configure an extension number and point it to an FXS port connected to a 66 block. From this 66 block it goes to a 6 zone paging system which is separate from the AVVID with the exception of the FXS port. Basically it is like sending a specific extension to an external analog line. From there, you go to your paging system. It seems to work really well.
There are a couple of different solutions that I have seen used. There are several 3rd party solutions (Twisted Pair & Berbee, to name two) that will perform paging through the Services interface. If you did not want to purchase a 3rd party solution, you can try a method that some Cisco engineers tested as part of the Pilot project I am working on.
If you have line appearance real estate available on all of the phones, you could create a shared line appearance on the group of phones that you wanted paged. Set this appearance to auto-answer.
This will create a line on the phones that rings once, then automatically picks up on the speakerphone. The paging party would simply pick up his handset, dial the extension number for the group he wanted to page, speak the page and disconnect.
Hope that helps,
My client has a 9-zone paging system, of which is connected to a universal paging access module. For the life of me I've been unable to successfully intergate the UPAM to the FXS. By any chance can you provide some additional info as to how you were able to do your integration?