NEC is a world leader in technology. It has a number of choices in telephone systems:
Aspire - an IP telephony solution with capacity of 8 to 100 users, uses MyCalls monitoring, etc.
XN120 - multiple extensions, connect to any type of phone, integrates to your PC, etc.
Univerge SV8100 - newest addition to the NEC range with capacity up to 500 users. Its expandability means it can work at any level, from a technically superb phone system, to a truly advanced unified communications platform.