Ancestry updates British Phone Books, 1880-1984

This database now contains 1780 phone books, 278 million entries, providing near full county coverage for England and substantial records for Scotland, Ireland, and Wales.

Alphabetical listings typically contain:

Surname of person (usually the head of household) or name of business
Address
Exchange (up to 1968)
Telephone Number

Note that you must enter a country through the drop-down menu, but if you try to enter a county as well the country selection disappears and the search fails. Instead enter the county in the location box.