I actually manage the Asterisk server at our work (and we have almost everything running on CentOS). I also maintain the Asterisk and related packages in the Atrpms repo. So I can help in setting up a server and maintaining it. I guess the main issue is if that besides VOIP access do we get it connected to the normal telephone network somehow and who is going to pay for that ? I'm using ISDN at work, but I'm pretty sure I can get the other stuff working as well.
Regards, Tim