Voice OVER IP PA system

A school recently contacted me about helping them setup a new PA system in the school as theirs died and they can no longer get any parts for it. They want to know (as do I) if they can use their existing CAT 5 cables that were recently installed and setup some sort of PA system using voice over IP? They also ideally would like to get the school's bell system on this as well so that the bells will ring at certain times throughout the day to dismiss the students. I know this is not really security related, but I was hopig someone on here (being that I really trust the opinions of those on here) to let me know if its even possible, what types of equipment would be needed and so forth.

is it possible? -- yes, however one caveat is that you have to tie it in with a phone system to use, so if the students figure out what the number is then they could get into it if the system is hooked into the outside world. the best way to do it would be setup a private VoIP VLAN using the routers and switches that are there already and not hook it to the outside world at all, then someone would have to hack the pop router and any subsequent router to get into the VoIP system -- and you could always put a firewall in there for good measure. look here for more info:

a possible tool:
http://www.talkswitch.com/download/t...r_Business.pdf
http://www.talkswitch.com/download/t..._datasheet.pdf

what you need to protect from:
http://www.phreaksandgeeks.com/pa.txt

Thanks for all the help...those are all excellent articles...
For now, the school does NOT want to tie their phone systems into this - and probably won't go with it if they have to do that at this point because of budget and cost constraints. Basically they are just thinking they can save a little $ by doing this since the school is already wired with Cat-5 cables to every room and every room already has ports and stuff setup. They may be wrong in that light as well about the saving money. They had a company quote them an old school PA system including wiring all new speaker wire and such for 25-30k. They said if they are spending that much, they'd like to consider making the PA system voice over IP if it could be done and not tie the phones to it (yet).

Well, with some effort and Linux guru skills, you could probably whip together an intercom system similar to DjScribble's suggestion, yet without a proprietary PBX system.

I'd explore Asterisk PBX http://www.asterisk.com and the VOIP Wiki at http://www.voip-info.org

I'd take a look at:
http://voip-info.org/tiki-index.php?...20phone%20door
and also
http://voip-info.org/wiki-Asterisk+paging+and+intercom

which whould inevitably lead you to:
http://www.digitalacoustics.com/lanplay.htm
Which sound's like exactly what you need without any Linux hacking and hardware manipulation.
I'd personally try to figure out how to do it with Asterisk, and then plan to stage out there current phone system into VOIP, but that is just me...

Hope this is helpful, I can't believe I stubled upon an actual VOIP intercom system, but then, I have a bookmark collection of VOIP stuff that is incredible since I'm hopefully going to be migrating my office over to some kind of VOIP PBX...

Well, elrey103, you've managed to get me at my most helpful on this board, now I better stop while I'm ahead.

Good luck,
Dhej