I am looking for data on historic telephone call prices in the US between 1920 and 1930. What did it cost to make a call? I know that, back then different rates were charged based on the distance of the call. But what where these rates? And what were the pricing categories at which different distances were bundled?
I have already searched the website of AT&T and the FCC as well as consulted articles and books in economic history but this information is surprisingly rare.
Edit: One source from the FCC (here, p. 62, table 13) shows the different rates charged for some specific distances. These are very helpful to get a good picture of the price differences. However, for my purpose it would be important to know at exactly which distances calls were classified as long-distance (or would fall in the next higher category) and thus become more expensive.