business telephone service
A business phone system that's delivered as a hosted service, typically by one of the major telephone companies. Frequently referred to as a centrex, a business telephone service can free companies from having to invest in the costly equipment of a complex private branch exchange (PBX).
With a business phone service multiple telephones are utilized in an interconnected fashion that allows for features like call handling and transferring, conference calling, call metering and accounting, private and shared voice message boxes, etc. Business telephone services can function over the Public Switched Telephone Network (PSTN) and/or over the Internet (Internet telephony or VoIP).