The good old phone book can be a genealogist's best friend. Telephone directories provide a detailed name and address listing (and phone number, of course). But beyond that, collections of phone books can bracket how long a person lived at a particular address, showing when their listing first appears, when it changes to a new address, and when it eventually disappears, as an ancestor moves out of town, or out of country, or passes on.
The Library of Congress has a wonderful hard-copy collection of European directories, largely focused on the decades just before and after WWII.
A few of their phone books from Eastern Europe have been digitized, and are fully available online:
- Bulgaria: Directories for 1917, 1919, 1945 and 1947 are available. These include various combinations of individual and business listings, as well as government officials. There are also sections with maps, photographs, information on royal families, and so on. Text is in Bulgarian and German.
- Poland: The Library has a 1923 business directory, as well as a 1939 directory of residential and business listings for Warsaw and the surrounding areas.
- Romania: This is the largest online collection of phone books, with intermittent coverage from 1923-1970. The books chiefly focus on the area around Bucharest, though there are listings for the rest of Romania as well.
Telephone books being what they are, these tend to be very large files if you try to download the entire directory. However, the LoC makes the directories available in a page viewer that allows you to flip through the content without having to download the entire volume. Very handy.
Looking for more historical directories? Check out the online collection at the Genealogy Indexer, which covers mostly Eastern Europe, but has a bit of material from the UK, France, and South America as well.
Don't forget to also check for your family history at Ancestry.com and NewspaperArchive. These are subscription databases, but they are among the most powerful research tools available for looking into family roots.