BT is putting its entire archive of old phone books online for genealogists, or anyone else, to browse. The phone books date back to 1880 and contain 280 million names. They can be used to track down relatives, but you can also use the service to find out if your house has ever had any famous, or infamous, residents.
The first phone book contained 248 names but no numbers - callers were expected to call the operator to get connected.
All books before BT's privatisation are public records. The service is available through http://www.ancestry.co.uk.