Have you ever had a phone number but not a name?
There are two kinds of phone directories, ones with the entries ordered by name alphabetically or by subject and ones with entries ordered by number or by location. These are called "reverse directories" and can be very useful when you want to find the information attached to a number or an address.
The Magazines and Newspapers Center holds two kinds of "reverse directory" reference sources. The first are print resources called the Polk's Directory, 1953-1982, and The Haines Directory, 1976 - Current, and the AT&T Street Addresss Telephone Directory. All of these directories are available at the Center's Reference Desk. These directories are extremely helpful--and sometimes full of surprises-- to genealogical researchers.
The second kind of reverse directory is the Reference USA database where you can enter a ten digit number and perform a search. Reference USA comprises the library's largest telephone reference source and holds over 14 million business numbers and 210 million residential numbers in the United States.