The BT Archive has now put their catalogue online. You can search through the catalogued entries for documents, books, objects, images and films on subjects spanning the development of telecommunications, from the birth of the electric telegraph in the 1830s to the explosion of the internet and the rise of competition. The catalogue will be updated regularly with descriptions of additional material.
http://www.btplc.com/Thegroup/BTsHistory/BTgrouparchives/index.htm
