Poplar1,
I believe you are correct about the door-bell-type button being momentary.
On page 6 of the document from 1947 at:
http://www.telephonecollectors.info/strombergcarlson/selectophone/PDF/KG_1947_BLTN_815_MN_SELECTOPHONE.pdf , in a section entitled, “A Brief Description of Select-O-Phone, The Private Automatic Telephone System”, I found the following statement which is the
first statement I have been able to find that seems to talk about the door-bell-type button that appears on many of the Redbars.
''''''''''''''''''''''''''''''''''
“7. Party Line Service
…To ring a station on your own party line, merely press the ringing button; the dial need not be operated. Conversations between stations on a party line are as private as between stations on single station lines.”
''''''''''''''''''''''''''''''''''
So I guess that it just rings the bells of the phones in the system that are on the same party line circuit that it is on. (I am making a guess here as I am really not very familiar with how telephone systems are put together.)
I assume that if I knew where to look for it (and I was better at spotting things on a schematic), it must show up on the Select-O-Phone schematics.
