Before PABX came alongside, firms needed to use human operators to connect calls by hand. This process was time-consuming and lacked performance. PABX systems made this complete system automated. PBX and PABX are both personal telephone networks. The terms are sometimes used interchangeably when referring to non-public business telephone networks. https://cpanelserver2.total-blog.com/the-ultimate-guide-to-pabx-systems-60883802