Evolve your communications with 3CX Phone System for Windows - an IP Phone System that completely replaces your proprietary PBX, supports standard SIP soft/hard phones, VOIP services and traditional PSTN phone lines. 3CX Phone System is far less expensive than a traditional PBX and can reduce call costs substantially by using a VOIP service provider. Its web-based administration makes phone system management easy. 3CX Phone System eliminates the phone wiring network and allows users to hot desk simply by taking their phone.

Key Features:

Complete phone system - Provides call switching, routing & queueing
Purchase cost dramatically lower than a traditional hardware PBX
Scaleable - Unlimited extensions and phone lines. No proprietary expansion modules needed!
Web based configuration & status indication - Easy phone system management!
Unified messaging - Receive voice mail via e-mail
Auto attendant (e.g. 1 for sales, 2 for support, etc.)
Reduce long distance and inter office call costs
No more expensive proprietary system phones - Use standard SIP phones
Eliminate the phone wiring and make moving offices easier
Out of the box configuration for many VOIP providers

Article Source: http://www.3cx.com/phone-system/