Internet protocol, bringing benefits for computer telephony integration (CTI). An IP-PBX can exist as physical hardware, or can carry out its functions virtually, performing the call-routing activities of the traditional PBX or key system as a software system. The virtual version is also called a "Soft PBX". See also Centrex Circuit ID Cloud communications Ground start trunk List of SIP software RJ21 Switchboard operator Telephone exchange Telephone switchboards References External links Telephone exchange equipment Computer telephony integration Telephony equipment