The development of the push-button telephone was merely done at Bell Labs, with the DTMF system being invented in 1959. The 10-button layout was the result of extensive user research by John E. Karlin and his team at the Human Factors Engineering Department of Bell Labs in 1963. The original design did not include the * and # keys, which were added later to facilitate additional functionality. Plus, DTMF phones were able to generate 12 different tone patterns (3×4 matrix), so why not add 2 buttons for future use. It was until 1968 that 10 buttons were quite common. So far history…

Below is a picture of a set Ericofon parts that I got this week. This is just a part of the whole set, but at least the most interesting part.

So what do we’ve got here? Two NOS shells, a non-wired Touch Tone chassis, some chassis plastics, some dial faces, an extra horse shoe switch and a few ear caps. Let’s have a closer look.

The 2 shells are full Touch Tone shells, but… they do not have any holes for the microphone (yet). My best guess is that they were taken from production to be used for assembling the Touch Tone in an early stage.

Two of the 3 ear caps are still on their production reel. The chassis with the dial-face only has 10 buttons and it is not wired. It is just the mechanical basics. On top of that, the keys do not have any print on them.

On the bottom left picture you can see 2 horseshoe switches. A regular one (on the table) and one from this set (on top of the other). You can see that the length is different which also reflects in a post I made earlier.This also means that the dial-faces of the 10 and 12 button version have different shapes as you can see. Not only that, also the plastic chassis part is different. The last picture shows a 12 button wired chassis versus this one. The shapes differ in quite a lot details.

It seems that the set I bought is a set with some prototyping material, that must be obvious. It is considered that a 10 button Touch Tone Ericofon is a prototype. There has been no reference to this type of keypad in any Ericofon documentation and as far as known they were never sold. They were introduced with 12 buttons from the start. Although a fancy dial-face with 10 buttons exists.

All with all I was quite positively surprised when I got the box with this material in the mail. As it normally goes in online buys, the pictures are not always very clear.

I have assembled 1 prototype, so I can add it to my collection. The transparent dial-face I like the most 🙂