One calls 264-0044 and gets a tone, interrupted every 20 seconds or so. This tone is measured in Decibels by special equipment. In this case, it was 264-0045. The tone goes away, and both people can talk to each other. For testing, one inserts the 1000 Hz tone, and measures the level at the other end to get the line loss on both sides.
Some loops are free.
Naturally, billing hasn't started yet.