In the 1970s the telcos were under pressure between increased costs from inflation and regulators who didn't allow rate hikes. They found that Directory Assistance was a big cost and that customers were abusing it -- using it for numbers not found in the phone book. Also, as described, calls for unlisted numbers took up much operator's time. So instead of a general rate hike, they started more a la carte charging which the commissions would accept. Some businesses used Directory Assistance as a free address verification service. Likewise, long distance directory assistance (NPA+555+1212) used to be free became charged and now is about a $1/pop with questionable reliability.
Note that Bell System rates and policies were not at all uniform nation wide. Some areas charged for unlisted numbers long before others did. The various service plans and local calling area sizes varied from town to town as much as 25%. Philadelphia seemed to have the lowest rates and most generous terms yet excellent service quality, how this was managed I don't know. Conversely, NYC seemed to have high rates yet poor service quality. I think Chicago was in the middle. [Pat--could a Chicago residence get flat rate service? Did it cover the whole city or only a portion?]
Almost exactly one hundred years ago (3/23/07, NYT) a citizen asked that the phone company put in a thumb index in the telephone directory to speed up searching. (A thumb index is often found in large dictionaires and consists of an edge cutout to speed finding the pages of a certain letter.) AFAIK the request was denied. Interesting how issues haven't changed even over 100 years!
[TELECOM Digest Editor's Note: Chicago had one unit per call, no matter what the distance was (within Chicago) for many years, as did all the suburbs. Then someone noticed that none of the suburbs were anywhere as large or geographically wide spread as the city itself. For example, from a corner of the city's northwest side, near the airport but within the city, to 134th Street and Avenue J is a total distance of 35 miles; all within the same city. On the other hand, many suburbs were two blocks long and three blocks wide for the entire town. So, about ten years ago, telco divided up all of 312/773/708/630/847 into 'zones' where the local central office was up to seven or eight miles away. _That_ then became your 'unlimited calling area' for one untimed unit; area codes did not matter any longer regards rates. So many of the suburbs now got three or four little towns surrounding them as part of their local calling area; living in Chicago, I got Chicago-Rogers Park, Chicago-Irving, and Chicago-Edgewater as my 'local untimed calling area'. The only people who beefed about that new arrangement were Chicago-ites of course who suddenly found they had to pay 'long distance toll rates' to call the other side of the same town.What got Illinois Bell greviously annoyed was back in the days when all LD directory assistance was totally free; remember those days? People with outbound WATS lines (who were charged per minute of connect time for all calls, including AC-555-1212) and the users of Sprint/MCI in the early days also had to pay for 555-1212 were told by their respective supervisors, "if you need to find the correct number to dial, use your 'regular' phone; learn the number then hang up and call back using WATS/Sprint/MCI etc. I know at Amoco we were _forbidden_ to do any 555-1212 calls from our WATS lines. "Use Bell for 555-1212 because the call is 'free'" is what we were told; "then use MCI or the WATS line to place the actual call itself. Obviously, in the early days of DDD, Bell gave directory assistance for free as a drawing card, fully expecting to get the 'real call' afterward. PAT]