Sort of reminds me of "Party Lines" (No, not the selective ringing, multiple subscriber/line service) used by kids in the 1970s. "Party Lines" or test lines allowed multiple callers to dial in like a conference bridge. Seemed to be used extensively by kids to just chat or hang out via the telephone network.
More info: https://www.youtube.com/watch?v=gy9zziwcV2w