BT answerphone manuals can be downloaded at http://www.bt.com/customerservices/userguides.jsp?parentcat=cs_userguide
If you can't find the manual at the above url :-BT have introduced a charge for their instruction manuals which were previously free to customers. The charge is normally £5. To obtain one you will need to ring the company BT now use to supply manuals on 0800 980 8999.
Any manuals directly available from this site are listed below.