We had two lines - one listed, one unlisted for the hospital, answering service, or other select callers to use. We could use the listed number as much as we wanted.
We had an unlisted line as well, which was strictly for “official business”, but a lot of calls still came in on the listed number.
The three-minute limit was pretty much impossible to maintain once we reached adolescence, though Dad would still grumble about tying up the phone.