If you are looking for a new phone system, consider getting an Asterisk PBX.  Asterisk is an open source project (www.astersik.org).  The system is free except for the hardware needed to run it.  Here's what you need to set up a 50 phone system (for systems with 10 to 50 phones, the following hardware is still accurate.  below 10 phones, a different quote needs to be made).

• $2500 - Server: Dual processor and dual core with 2GB RAM, 2 300GB SATA Drives, Supermicro motherboard, etc).
• $1500 - Phone Board: (Digi - get a good one with hardware that handles echo cancellation...usually these boards are less than $1500).
• $10,000 - 50 Phones: There are cheap phones available for $75 each, but you should get a phone at around $200 to get better quality conversations.  If you want extravagant features get a phone that costs $300.
• $1250 - Network Switches w/ POE: Upgrade your network switches to include Power Over Ethernet (POE).  This keeps you from having to plug your phone into the electric plug and the network.  Date and power will be supplied through the same cable.  Linksys Layer 2 POE 24 port switches (12 of the 24 ports are POE) cost about $250.  You will need 4 to 5 each.
• $15,750 Total Cost.

Most VOIP phone systems of this size cost $30,000 and up.  Nortel costs above $60,000. I recommend having an experienced professional configure the system.  BNSC can get this size system up and running for $1000.  Some local contractors ma do it for less.  BNSC will install the software, test the phones, configure the extensions, configure the voice mail, set the call pattern/plan, send you the system and walk you through the placement of the boxes and phones by phone call.  We will also train key members of your staff.  BNSC can be on location for travel costs plus $650/day (estimating 10 hours per day of worktime).