communications (PBX) A telephone exchange local to a particular organisation who use, rather than provide, telephone services. The earliest PBXs were manual (Private Manual Branch EXchange, PMBX) but are now more likely to be automatic (Private Automatic Branch eXchange). (1997-06-25)
There was a private branch exchange there, and Alice knew the girl operator.
It was the period of the message rate, the pay station, the farm line, and the private branch exchange.