In a message dated 10/30/05 4:59:45 PM Central Standard Time, snipped-for-privacy@telecom-digest.org writes in response to a posting from C_shore :
[TELECOM Digest Editor's Note: They were in use beginning sometime in
> the early to middle 1960's, but they were not the little plastic things
> which plug in and snap out like today. They were four-prong metal
> things with a plastic cover; they more closely resembled wall outlets
> for electrical cords. My private phone line at Windermere Hotel in
> 1963-64 (HYDe Park 3714)had one, although the 'house' phone (off of
> the Windermere switchboard) was hard wired. When I eventually got a
> new 'two line phone' (turn button to select desired line, either
> private line or switchboard) to go in my bedroom, that one also had an
> RJ connector, I think either 1965 or 1966.) PAT]
The four-prong connectors you describe were not RJ connectors. They date from a least before World War II and were the common method of making telephones portable.
The RJ (modular) connectors came much later; in fact, you can I think still buy adapters with a RJ connector on the back of the four-prong plug so you don't have to replace your hard-wired four-prong jack.
The four-prong jack was used only for the mounting cord. Modular jacks and plugs are used today for the handset cord and various other purposes as well; the four-prong plug and jack are clearly unsuitable for that.
Wes Leatherock snipped-for-privacy@aol.com snipped-for-privacy@yahoo.com