Phone System Evolution

In the early 20th century, every textile tycoon and railroad baron had a collection of tall black “candlestick” phones on top of his desk. When a phone rang, his frazzled secretary scrambled to pick the right one. While wheeling and dealing with one guy, and a call came in from another guy, Mr. Big stuck the first phone in a drawer or file cabinet to keep his secrets from being overheard. This was not very efficient.

In the middle of the roaring twenties, some phone company bright guy had a better idea. Instead of having a bunch of phones on one desk, he put a bunch of lines on one phone. This freed some desktop real estate and made life simpler for Fords, Vanderbilts, Carnegies and Wannabees.

To select a specific line, the boss or secretary could press a button. Perhaps because the button opened and closed a circuit, it was called a “key.” Or maybe it was called a key because pressing it reminded someone of pressing a piano key or a telegraph key. At any rate, multi-line phones became known as “key phones,” and the relays and wires and other stuff they got connected to, was called a “key telephone system” or “KTS” in Bell System lingo.

Over the next 50 years, key systems got more complex and more convenient, with new features like hold buttons, lights, intercoms, paging, speakerphones, privacy, music-on-hold, long-distance restriction, timers and memory dialing — from AT&T and a growing number of worldwide competitors. But despite many companies offering a huge variety of systems and accessories, these “electromechanical” key systems had one thing in common: a lot of wires.

There was a separate two-wire electrical circuit for each phone line, going from a central control box to each phone where that line was available. Most phones also had an additional pair of wires for the light that indicated the status of a line, and another pair for “A-lead control” which operated the light and the hold circuit. With six wires per line, a Call Director phone like President Kennedy used, with lots of lines, could require 150 wires in a clumsy cable as thick as a garden hose.

That cable was not pretty to look at, and was no picnic to install. Technicians cursed each wire, and the chances of putting a wire in the wrong place increased with the complexity of an installation. If a line or a light stopped working, finding the broken wire in a dark and crowded cable closet could be an all-day affair; and the more wires in the closet, the more likely that some of them would get broken, and stay broken.

AT&T’s ComKey 416, introduced in 1975, provided most of the features of phone systems that used a central control unit, without the control unit. The phone had modular construction, so malfunctioning subassemblies could be easily replaced. That central control unit was called a Key Service Unit (KSU), so the ComKey 416 was the forerunner of modern “KSU-less” systems, like the Panasonic KX-T3282.

Meanwhile, there were businesses that had lots of phone lines, but just one simple pair of wires going to just one simple phone on each desk. They were connected to a PBX system (“Private Branch Exchange”) which was a smaller version of the phone company’s Central Office exchange. Like the Central Office, the PBX originally depended on a switchboard operator, like Lily Tomlin in her Ernestine role, whom everyone hoped would put each plug in the right jack, and would allow people to talk and make mon-ey. The hordes of operators that were needed to provide a growing number of connections got expensive and unreliable, and required lots of space and creature comforts; so both Central Offices and ordinary offices got automated.

The PABX (with the “A” standing for “automatic”) still needed an operator or receptionist to direct incoming calls to the right people, but you could get a dial tone to make a call by simply dialing 9 instead of begging Betty to plug you in; and by dialing other digits, you could call others within the business.

Fancier PABXs allowed users to put calls on hold, trans-fer calls to other departments, set up multi-person confer-ence calls, dial numbers from memory, choose specific lines for specific calls, and create records of calling costs.

These fancier features could be handled by plain-Jane phones working on just one pair of wires, but the system still needed Jane or Betty or Ernestine to sit at a console and direct incoming calls to the right people. And you’d better make sure that someone else could cover for her at lunch time and sick time and vacation time.

On the other hand, companies using key systems did not need dedicated ladies to answer the phone. Tom, Dick and Harry could answer any line on their multi-button phones, and then put the call on hold and yell “It’s for you.” The world was heading for a collision. Convenient key phones saved money by eliminating the expensive switch-board operator, but the heavy cables were expensive to in-stall, modify, and repair.

Instead of a collision, there was a solution — a technical solution. In the late 1970’s, a number of innovative companies developed electronic key systems that used inexpensive and easy-to-install “skinny wire” with just four-to-eight copper strands instead of dozens or hundreds. This made life much easier for installers, which meant that installations could be cheaper and more reliable for the phone system’s owner.

Simultaneous advances in microcircuitry allowed formerly-expensive add-ons, like speakerphones and SMDR (“Station Message Detail Recording”), to be included for just a few extra bucks.

The “architecture” of electronic key systems is more like PBXs than electromechanical key systems.

With older “1A2” electromechanical phone systems, there is usually a discrete copper wire path for each phone line from the phone company, through your phone system’s control unit, to the phone on your desk. You press a button (“key”) on your phone to select which line passes through the phone base to the handset, so you can talk. With a modern PBX or electronic key system, pressing a button commands your control unit to connect you to a spe-cific line. Even though only one line is “inside” your phone at any given time, you can instantly switch to another line. The button makes a momentary connection to set up a talking path, instead of being mechanically latched with a failure-prone linkage of levers and springs. In place of incandescent bulbs that start burning out the first time they light up, modern phones use Liquid Crystal Displays (“LCDs”) and Light-Emitting Diodes (“LEDs”) that use less power than bulbs, and should still be shining brightly when the Klingons finally make peace with the United Federation of Planets.

The central control box that provides brain power for a key system has shrunken from the size of a file cabinet to a medicine cabinet (or even smaller), and is cooler, quieter, and has very few moving parts to wear out. Adding additional lines, phones and features usually re-quires just plugging in a circuit pack or a printed circuit board (PCB), instead of connecting dozens and dozens of accursed wires.

Electronic phone systems could be wonderful, but many early models stunk. Some products were put on the market before they had been fully developed, others had strange responses to particular kinds of wire or environmental fac-tors, and some were simply overpriced or under-built.

But by the early 1980s, there were plenty of superb electronic systems around. Some, such as those sold by TIE and Asuzi were also particularly good values, and they eventually won over the hearts and minds of even the most retrograde cynics. Very few companies sell or use electromechanical phone systems now, but the traditional phones are still found on David Letterman’s desk and in government offices.


The excitement today, is in phone systems that are not just electronic, but digital.

“Digital” means more than having a display panel that shows the time and the number dialed. “Digital” has been the major buzzword in the electronics industry for over a decade, but few people outside the business understand the technology or its benefits.

Complex numerical data, printed and spoken words, even music and moving color pictures, can be represented by a series of ones and zeroes, and then be stored, manipulated, transmitted, received and perfectly reproduced.

This technology is responsible for a wide range of new and improved products and services, such as noise-free mu-sic on compact discs, super-sharp direct-from-satellite tele-vision, complex video games, movie special effects, your PC, quiet car phones, faster faxing and voicemail.

In office phone systems, digital technology has led to the development of multi-line, multi-feature phones that use just two wires (one “pair”), instead of the four or more wires that used to be needed.

Traditional electronic phone systems used one pair for voice plus one for data (such as instructions for connecting lines and turning on lights), and maybe a third pair for off-hook call announcing.

Digital phones convert voice into data, so it can flow through the same wires as other information and instructions and even power. Digital phone systems generally have more features than analog systems.

For most people, digital vs. analog simply should not matter. It’s a distinction without a difference.

In a business or home phone system, one technology does not sound better or provide more reliable telecommunications than the other. Digital phone systems have some analog components. Analog phone systems have lots of digital circuitry. Make your decision based on features, esthetics and price, not buzzwords or snobbery.

Above eight lines, most current phone systems are digital, not analog.

Most phone manufacturers have digital products today. Some evolved from earlier analog systems. Others were completely new designs. Analog system development has not stood still, however. One recent trend is a growing number of feature-rich “KSU-less” systems that provide simple installation by eliminating the control unit.

There is also a growing popularity in “hybrid” phone systems that combine features of both key systems and PBX systems, and can work with both multi-line phones and single-line phones.

If a person or department isn’t very important, you plug in a $25 phone, and it works PBX-style, by dialing nine for outside dial tone. If the person or department gets more important, the inexpensive phone can easily be replaced with a fancier model that works key-system-style, with lights and buttons and a speaker and maybe an alphanumeric display.

What’s ahead?

You can expect more interaction between phones and computers, more "IP" phones that work as part of computer net-works, and more phone systems that don’t need wires between the phones.