The Private Branch Exchange… the No Frills Approach for Saving Money on your Telephone Bills!

In the wayback of time, in the days of electromechanical switching, and you had say a 500 users… what was your options?

There was two options. Centrex and a PBX. What was the difference? One was off prem at the phone company and the other was just an identical copy of a switch, just a bit modified for an on premise environment. I should also state, that back in those days, it was not abnormal for PBX systems to be in sites less than 200 phones. The role of a PBX at the time was to have less cabling going in, allowing users to call each other by a 3 to 4 digit numbers, and be able to access to the outside world… but in those days most of the PBX was done by humans…

The operator switchboard was basically the “PBX” while in the switchrooms, was all the switching of the time whether it was crossbar or Step by Step. There was not that many features, and that didn’t come till the days of ROLM, Northern’s SL1 and AT&T’s Dimension.

There was “Cordless switchboards” that resembled the Call Directors, but it was done in a similar fashion, a call would come into a bank of lines, and the operator would buzz the extension to then patch them in via buttons. But a cordless switchboard was still a very wiring intensive devices, with many, many pairs of wires that had to be tied directly to the console.

So what about outbound calling? Before the days of electronics, a user would “dial zero” and ask to dial out, the operator would patch that caller, and either s/he would dial, or if the operator was nice, would dial the number for that caller.

The cost of a PBX, to users to lines was still cheaper, but was mostly seen in hotels, and some businesses where handling calls were important. The 1970s that brought the ability to have multiple phones and few lines coming from the telco, also brought features like station IDs (internal caller ID), Automatic Routing Selections and Automatic Alternative Routing, and anything where a computer could hear the tones and or rotary pulses where the PBX could dial for the user, rather than an operator. This moved the dialing into an electronic mainframe, but the operator still had a role to play, to answer calls, to juggle calls, and to monitor the health of the electronic PBX, sometimes outside of the States it’s called “Private Automatic Branch Exchange”.

A lot of these PBX systems were phased out with the advent of electronics by the late 1970s, but there were holdouts up to the 90s. The White House had zero electronic systems until the Clinton administration that by the mid 1990s had installed then an AT&T Definity PBX; that only had a shelf life of 3 Presidents dual terms. By 2017, the Trump Administration had prided for having a “very secure” phone system that was a Cisco, which had been a secondary system since the latter end of the Bush administration.

If you are a Gen Xer and older, you could tell a system was a PBX or Centrex by telling it’s telephone.

Standard one line phones were common in PBX setups even in the days of electronic.

If you did see Key phones, most likely it was because they were the power users, and needed direct access to lines without operators or codes. While some say the 1A2 concept was dated by the advent of electronic systems, this was critical in places where calls couldn’t get dropped because a transfer failed. In the advent of VOIP, the physics of how a call can be captured or be answered or a line can be captured… and that can be blamed to the lack of listening to customers in the world of IP… but that happened many years later.