The NYT had an article about the German telephone directory listing of actress/singer Marlene Dietrich. The article included a scan and explanation of the directory page.
Article:Page Scan: While the article provides a general explantion of the listing, if anyone is familiar with the exchange layout perhaps they could add some additional comments.
The article mentioned that some old phone books are being digitized for ancestral research. This seems very interesting.
I knew someone with a 50 year old phone book of my city and going through the old listings was quite interesting. For families and people that I knew, most were living in the old neighborhood.
Also of interest was a comparison between the old directory and the current one. We could see for some names a man in the old neighborhood vs. a woman's name in a senior apartment, presumably the widow of the man in the old listing. We saw a surprising number of listings that hadn't changed in 50 years, and many where the name/ address was the same though the number was different. In the new directory we saw new ethnicities that weren't in the city 50 years ago.
In a very old phone book, I saw a church whose number was unchanged from 1923 to today. Back then it was merely '29', today it is nnx-0029.