We would probably still be without call display, were it not for the fact that a few years ago our phone number got onto a list of fax numbers that was distributed on a CD, undoubtedly for a price, to entities who wished to advertise by fax. Many such entities at the time were not careful of the regulations applying to such use, and sent their #$&#&#^&$*$&*$^*$^&*$ faxes at all times of day and night, and we were regularly woken up at some ungodly hour, only to hear at the other end of the phone, "BEEP...BEEP...BEEP...BEEP...BEEP..." You get the picture. At the time, my Dad (then 80+)was still living downstairs from us, so no way could we just turn the ringer off, in case he had an emergency in the middle of the night.
It took a LOT of logging of calls, a LOT of correspondence with the phone company and CRTC, etc, to get the situation settled down. In the process, we got (among other things) call display, so we could at least not pick up calls from numbers we didn't recognize. We still get a few such calls every week, but not in the middle of the night anymore, thank God! And I've come to appreciate the screening capability -- and the ability to look at the number and answer "Hi Tom!"