The Telephone Number Directory web service allows you to directory style queries to the BT OSIS database. A directory style query is one where you know approximate name and approximate address and you are prepared to have a list of matches returned rather than one distinctive answer. If you know the full name and address of the person you are searching then you should use the Telephone Number Capture service.
The Telephone Number Directory service can be accessed at http://webservices.data-8.co.uk/TelephoneDirectory.asmx.
To find out more you can use the below links