The IPx Office is the smallest system and offers a "all in one box" kind of solution with WLAN and router options. The other systems FlexiCom and IPx series go up to 6000 ports but can be networked for as many as you want. There's also the new Coral Sea Softswitch which has no limit on the number of users
http://www.tadirantele.com/solutions...oftswitch.aspx and is a completely new, build from the ground up, SIP based solution that can use the existing systems as connections to standard TDM equipment.