From what I coul read you definitely need an upgrade, you can definitely find cost effective solutions today. The key question will be how much is your company willing to invest? and how much in house control wants to keep.
This will derive into 2 scenarios 1) IP Centrex, meaning full PBX functionality provided via internet, you will need a realiable internet link and IP phones. 2) A ip pbx solution in house.
Mind you, other than more functionality VoIP will bring great savings if you use long distance.
Let me know if I can further assit you, this is in fact my core busines and can provide either solution.
Wolfgang wploch@rkmus.com