In the Bell System, ground start was never used for residential service. On two-party lines, the "tip" party would be wired with the ringer (and, on occasion, a portion of the hybrid coil) connected between the tip lead and ground, without an isolating capacitor, to allow the CO to determine the billing party. If there was current flow to ground, then the "tip" party was making the call.
I worked in a 5XB office once: IIRC, tips vs. ring id was made by the originating marker, but all other billing decisions were handled in the mainframes after the paper tape rolls had been sent out for offline processing.
I never worked on multi-line phones; they weren't available in my area when I was in the CO. However, I remember that we had a few "legacy" four-party lines, and I think (Again, IIRC) that billing was handled by CAMA operators asking for the originating number during billable calls.
[snip]William
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