In today's dollars, the cost differential was about $15-$25 per month. For a family of modest means, that extra $15 each month adds up; certainly $25 adds up.
In the 1950s, plenty of people had two or even four party service, again due to the cost savings. My parents had message rate / two party service back then; later on they switched to private line unlimited. They were able to do this because phone rates were stable while salaries were increasing.
It's a tricky question because for an analysis to be accurate, all prices must be adjusted for inflation. Many phone rates essentially went down due to inflation even if the dollar amount remained constant.
In the case of long distance rates, after WW II each rate decrease generated higher demand. The Bell System developed higher capacity inter-city trunks (coax, microwave, carrier) which created economies of scale. The cost per individual call dropped.
I came across a Western Union ad from the mid 1950s claiming the telegram was cheaper than the typical long distance call; with a chart of costs. Around 1960 or so long distance rates dropped while telegraph rates went up and a phone call became cheaper than a telegram.