Browsing through the Staten Island, NY telephone directory of January 1940, I found that certain phone numbers were printed with a suffix J, M, R or W. What do these mean? I've marked a few of them in the image below.
The phone book itself does not define these suffixes -- I checked carefully. These letters do not seem to represent calling rate zones, as Staten Island had only two zones.
Party lines? I'm aware that up to 4 customers could share a phone number and each would get a distinctive ring so the correct party would know to pick up, but I've never known how one would call a particular party on a party line. This phone book mentions that "party lines are available" but gives no further information about them.


"party line" "morse code"returns several anecdotes where people (in the US, but not, as far as I can see, New York) say they had those letters & ring tones (including -J) for party lines when they were young. It also returns the Wikipedia article on Party lines which states that letters & their corresponding morse codes were used for (at least some) party lines in Australia – sempaiscuba May 22 '20 at 07:22