I worked for MCI in the '80s. People changed over for the savings - it was always cheaper than AT&T. In fact, a lot of AT&T's marketing played to the "loyalty" fear: if you leave us, you're suspect for being un-American. Not in so many words, of course, but that was the tuning fork it resonated with. (Worked great on older folks who lived through McCarthyism.)

Also, don't forget the difference between inter-LATA and intra-LATA calls. The latter was a call within your local provider's area, the former went to another. Sometimes the line between exchanges was literally across the road. Inter-LATA calls were generally more expensive than getting through on a long-distance trunk, so there was this ridiculous feature of phone bills in those days that calling grandma in the next town over was more expensive than calling your college girlfriend three states away.

I also used to work for a "connected car" manufacturer. The per-minute rates they get today for using the onboard phone are outrageous even by '80s standards. I won't mention the data rates they charge for using the "connected car." Let's just say it would be far cheaper to buy an iPhone and Verizon's 20GB plan if you're going to use it a lot.