They were billed at the outgoing end, handled at the local exchange for the most part. Handled offline until quite late at a lot of them -- think rolls of pape

They were billed at the outgoing end, handled at the local exchange for the most part. Handled offline until quite late at a lot of them -- think rolls of paper tapes (later magtape) logging calls, to be read in at the billing office at the end of the month. You'd still have to know which exchange the call was coming from, to track it that way.