Standard phone connections are RED / GREEN for the line 1, YELLOW / BLACK for line 2 - today. Ring and tip are the same today as they were with rotary phones before since there are still people with rotary phones in use combined with touch tone - there are actually touch-tone phones that have switches on them to get them to output 'pulses' instead of tones. My father-in-law here on the farm refuses to pay 'extra' for touch-tone service, so he has the basic with a button phone that outputs pulses.
When that 4-square was installed, yellow / black were probably not used as multi-line households were totally unheard-of. As mentioned, sometimes those connectors were used for power to 'lighted dials' and would have a small power supply connected at the interface surge supressor demark or somewhere in the house where 110 vac power was available to 'inject'.
That 4-square was not restricted to 'rotary' phones.
There were many touch-tone phones built with that jack until about 1975, when the phone company decided to go to the 'modular' system currently used.
Remember when touch-tones phones were introduced to the public? NYC World's Fair, 1964 in the public pay phone booths. After the first week, almost all had been ripped out and stolen by people that didn't realize that they could not use them at home. Ma Bell had to put up signs explaining that theft was of no use - phone would not work.
Last I looked, RadioShack still SOLD a converter from 4-square to modular.
The problem with connecting OLD phones is not one of the connection, but one of 'ring equivalency' - the power necessary to make the bell ring. If the RE is too high (or the total RE for the house is too high), the phone company may not be able to send enough current down the new lines at 68 VDC to make the bell ring.
This isn't a problem with the new electronic phones, but the old phones took quite a lot of 68VDC to cause the bell to function.
If you have a phone with a magneto in it, you do NOT want to connect it to the telephone system.
When you spin the magneto, the phone sent voltage BACK to to the switchboard to let the operator know you wanted to make a call. Sending voltage BACK DOWN a phone line today will cause major problems at the phone company end and may very well damage any phones you have connected in your own house.
Theoretically, the phone company should protect itself (lightning and all that), but there is no guarantee that any of the phones in your house have any protection, and if you spin the magneto hard enough to exceed the 'nominal' 68 VDC that the phones are designed to handle - you have just become the local RadioShack's best customer.