The BT Archives historical phone book collection is now available (or will be soon, I can't find a date) on the Ancestry Library Edition of Ancestry.com. According to the article (Public Libraries March/April 2007 Edition), more than 270 million names are listed, and you can search by name, year, and county.
Don't hold me to this, but I think you have to pay for Ancestry.com unless you get it through your library.
Don't hold me to this, but I think you have to pay for Ancestry.com unless you get it through your library.