In the past, although I’m sure there are details of which I am unaware, it was easy enough to understand how the telephone books were assembled. With (usually) just one choice of carrier, one entity had everyone’s number and could easily enough (sort of, I suppose) assemble the information and put out a phone book for all their customers to use. Pretty much the same scenario holds for directory assistance.
Now, with various carriers on the scene, the old pre-deregulation carrier still provides directory assistance and a phone book - at least in my area, where we all had Southwestern Bell (GTE did have a small, notably quirky presence). The new Southwestern Bell phone book lists every number I could think of to look up, including some that I know to be with alternate carriers, as well as alternate carriers themselves. And directory assistance seems to work for all working numbers.
So I would think that there is some industry-wide cooperation going on; how does that work?
How does it work? Unfortunately not so good anymore.
First some basics. Several years ago, in a landmark case, it was ruled that the listings in telephone books are not protected by copyrights. They are just lists and contain no creative content. Hence anyone can take a phone book, run it thru an automatic scanner with OCR, and get an electronic copy of a phone book.
Most phone co.s recognized the futility of trying to “protect” their listings in these circumstances and were amenable to sharing listings with other phone co.s This allowed better than once a year updates on listings for example. Other advantages include less arguments with operators: “So what if they’re GTE and not X-Bell, just tell me their d**n number!” Operator time is money.
But with the flourishing of various local, wireless, long distance and Internet phone services, this cooperation is breaking down. Some of these companies are getting irrational and not providing listings to despised competitors. Extremely bad business decision.
It might be that the PUCs in some states require such sharing and you might not notice it in your area, but I’ve seen Usenet posts where people complain about long distance information from one carrier not being able to provide numbers for certain unaffiliated local providers. Stupid, stupid, stupid.