So having a monopoly isn’t a competitive game changer in your book? The yellow book rates should have been regulated just like the phone rates. Once a monopoly is given, it is incumbent upon regulators to regulate. The customers were paying the company to receive annual phone books, so every dollar of ad revenue was profit. All competitors would clearly be on different ground.
I’m not sure you understand the phone book business at all. Any company at any time could have printed a book and sent it to everyone in an area, these competitors that did send a book did not charge people to have the book, they were published and delivered for free.