It was more than just the phone books. Back before smart phones, if you needed to look up a phone number you'd call information (411) and they'd look it up for you. For instance, if you were stuck on the side of the road and needed a tow truck.
Information would be able to look up businesses close to where you were using the NPA/NXX of the phone number you were calling from (the first six digits of the number including the area code) and then give you a couple options in alphabetical order.
I had a client who had a phone number in every exchange in NYC and had a name like "AAA Towing" so no matter where in NYC you called information for a tow truck from, they'd usually be the first option given to you.
The gunslinger is definitely a hard one to get going (but it does get going) because he was super young when he wrote it (I think he was like 19 or something like that) but overall the Dark Tower series is one of the best pieces of fiction I've ever read. Especially if you're familiar with his world building (lots of books live within the Dark Tower universe like The Stand, Salem's Lot, even The Shining to an extent). It also has one of the most memorable open lines of any book series "The man in black fled across the desert, and the gun slinger followed".