This definition appears very frequently
Samples in periodicals archive:
Some manufacturers of PABX (PBX) systems distinguish their products from others by creating new kinds of private branch exchanges. Rolm offers a Computerized Branch Exchange (CABX) and Usha Informatics offers an Electronic Private Automatic Branch Exchange.
As automated electromechanical switches and later electronic switching systems gradually replaced the manual systems, the terms private automatic branch exchange (PABX) and private manual branch exchange (PMBX) were used to differentiate them. Solid state digital systems were sometimes referred to as electronic private automatic branch exchanges (EPABX). Today, the term PBX is by far the most widely recognized.