UK phone directory
Search the UK phone directory by people or businesses. The full address is usually given. But you can't search from phone number to an address/person or find ex-directories.
International Guide - BT'd guide to international calss, codes, tariffs, etc.
Interpreting Phone Codes
Decode US, UK and other Prefix codes - Learn where a telephone prefix code is actually from (e.g. 01384 = Dudley). This very helpful American service works fine for the UK as well. Drop the first 0 of the area code and then prefix the rest with +44 for the UK. Dudley should be +44 1384. The response is impressive, with six valid locations given.
Finding or Interpreting UK Postcodes
Postcodes On Line - You can use this Royal Mail service to do up to fifty free searches per day to find postcodes, or to get approximate street addresses if the postcode is all you've got.
Fax for free
Get a free fax number - even if you don't have a fax machine. If anyone sends a fax to you, this service will be automatically convert it to an email attachment that comes straight to your mailbox. Note: you may need extra fax software on your computer if standard output quality is poor.