3CX is an open-platform, IP Telephony system that works with popular IP Phones and SIP trunks, whether on-premise or in the cloud. With 3CX, your telco phone bill will be slashed, and so will the cost of buying, expanding and maintaining your VoIP phone system. If you decide to host in the cloud you can self-host and pay a low monthly per PBX fee rather than an expensive per extension price per month.