What are the types of telephone switchboard and abbreviations?

There are several types of telephone switchboards, including Manual Switchboards (MSB), Centralized Automatic Switchboards (CAS), and Private Branch Exchanges (PBX). Manual switchboards require operators to connect calls manually, while CAS systems automatically route calls using digital or analog technology. PBX systems are used within organizations to manage internal and external calls efficiently. Common abbreviations include MSB, CAS, and PBX.