"Local" was another term for manual intercom. Unlike dial intercoms, which are self-explanatory, most local intercom setups on 1A2 used a simple 401A/B card to provide the talk path and lamp, then any type of momentary key could be used for signaling. If the phone had spare line keys, the locking pin could be removed and that key's A lead caused a ground to be sent to the distant buzzer when pressed. In the absence of spare line keys, an external line key was affixed to the side of the phone to provide the button(s) needed for the system.

I will say that I encountered some dial intercom setups that were designated as "local" too. That word was not exclusive to any particular type of intercom system. I'm pretty sure it was more about the person who was typing the labels for the phones.

While is was possible, the yellow/slate pair was rarely used for buzzer signaling. That pair was for the ringer. Buzzers could be on any pair, however the yellow/orange and yellow/green were most commonly used.

Ed Vaughn, MBSWWYPBX