Aside from the 'traditional' yellow pages falling into obsolescence they are usually void of pictures of the gals while also held under local, regional legal constraints.

up to a few years ago, when I was traveling to another city, I would use the phone book all the time and I did end up with some very nice providers.  

There was a clunker or two as well, but with TER and all the sites availiable on the internet now, there's no comparison.

Let's see should I use these stone knives and pointy sticks or this set of powerful tools?  

The net has SO much more information, not the least of which are the reviews.  Then there are LOTS of pictures and some even have videos.  Unless you like the adventure and risk, don't proceed without doing research, most notably READ the reviews.

But that was 25 years ago, when I started in this hobby.  Sure, you can get some great girls there, but it is truly like buying a "pig in a poke."   With the internet, you have photos (although with a number of girls and agencies they are fake--and I have seen my share of fakes)  But if you see a photo you like on the internet and can verify it with her reviews on TER, at least you know what you are getting before she shows up at your room or you at hers.

Phone book is great for local plumbers, painters, Doctors, but the internet is great for Research and Knowledge. Besides there are providers who might be in an hours drive where you have no access to the phonebook in those cities. The internet allows you to do the research across the country to cities where you might be visiting.

Seldom have I found phone book agencies to be reputable. I suggest you stay away from them. One method that I use to find an reliable escort in a city other than reviews is to examine the TER site reviews information, particularly that on escort agencies. Cities that have many agencies with good ratings usually have good environments for finding quality companions.
 The Net is superior to the phone book for the reasons stated above and also because Net phone numbers are fresh, numbers from a phone book can be outdated.