The Acumen IT Support blog provides you with helpful articles about the Windows-based 3CX VOIP phone system/PBX.
3CX is an open-standard, software based IP phone system that is accessible with popular IP phones and SIP trunks. A complete Unified Communications solution, this top of the line VoIP phone system is perfect for a business environment. It’s easy to use and compatible with a variety of operating systems, including Windows, Android and iPhone. 3CX also has a number of features, such as web conferencing and presence.
Several web sites provide good overviews.