Regarding party lines ... I remember "re-grouping" subscribers in rural Iowa about 20 years ago for GTE. When one or two party line subscribers would take the leap to a private line, we would put the remaining party line members onto another line. This would keep the party lines full, and if you had the lower cost party line, you at least had to put up with a full line. Some customers would "play the system" by waiting for their partymates to upgrade to a private line, then they would be left alone on a party line. If you weren't one of the old biddies, this was just great.
We didn't let this happen too often. It meant going out to the field and changing cable pairs on many folks, and we would sometimes have to use bridge lifters and bunching blocks in the CO to tie together various partymates. Of course, we had to keep good records (on paper, not computer at that time) in order to keep the right ringer frequencies together and so there wouldn't end up being two of the same frequency ringers on the same line. This was a case of trouble waiting to happen. With 4-party lines, you just had to keep track of who had a 20, 30, 40 and 50 cycle ringers. (We even had 60 cycle ringers in some exchanges, but that's another post). Early on in my career, and when I was a kid, I remember 8 party lines. You had the same ringer frequencies, but four were on one side of the line and four were on the other side, with the ground as the final ringer connection (grounded ringing).
Anyway, ringing configurations have been discussed at great length in previous years on the digest. Lisa's post just reminded me of the re-grouping we used to do.