What is this Alphanumeric Push Button Array marked 499e I found?

[allnumbedup]

I found this two X five pushbutton keyset array at a yard sale. There was nothing else like it there and no history or references I can find on-line. It is marked 499e.  The black face is painted metal and I think the keys have a celluloid feel like typewriter keys.  I think it may be from a switch board or piece of a switching station. The assginment of numbers to the keys makes me think this had a telephone application. The contacts appear to be meant to operate as momentary switches without being linked--just meant to pop up after signaling once being depressed. The is no ort of tone generator or pulse function. I thought the non-standard rectangular key array combined with the typical 'metropolitan' alphanumeric key assignment was oddball.  I would like to know what it is.

[poplar1]

Operator's position. Not DTMF (Touch-Tone).

[paul-f]

The 499E was one of several key units made for multi-frequency (MF) toll dialing, in use before DTMF was developed.

Some good background reading is in the Bell Laboratories Record article Multi-Frequency Pulsing, D. L. Moody. (December, 1945, p.466).

A bookmarked copy along with other related articles on crossbar switching and toll dialing is in the TCI Library here:
https://www.telephonecollectors.info/index.php/search?q=BLR+%22Crossbar+Toll+Reprint%22

[paul-f]

...I thought the non-standard rectangular key array combined with the typical 'metropolitan' alphanumeric key assignment was oddball...

Pushbutton dialing was logically used by operators long before being trusted for use by subscribers.

A first priority was speeding up the dialing speed of operators by replacing their rotary dials. Initially, as you noted, the circuitry was not part of the pushbutton mechanism, but was elsewhere in the switchboard.

There was a lot of research done later regarding the layout of pushbuttons for maximum dialing speed. A summary of an interesting 1941 Bell Labs study is included in the May, 2020 TCI Singing Wires article, Pushbutton Dial Layout Test - 1941.

A 1960 Bell System Technical Journal Article summarized eighteen layouts considered before the familiar 3x4 matrix was adopted. That and an article on the frequencies chosen can be found in the TCI Library with this search:
https://www.telephonecollectors.info/index.php/search?q=bstj+1960+pushbutton