[mcorning]

You are correct on both counts "Yellow Pages" was a registered trademark used in many countries for business phone numbers. Phone books also had literal yellow pages with business phone numbers and advertisements in them. It was also a colloquial term, at least where I am from (Midwest, USA) used to refer to the entire phone book.

It's funny how these weird pieces of knowledge stick even with almost zero exposure. Every time I got a phone book or yellow pages dropped on my doorstep in some flimsy transparent bag, I'd throw it directly into the recycle.