Hi, the ITU has issued a Technical Corrigendum to X.520 which adds the missing equality and substrings matching rules to the Facsimile Telephone Number attribute: http://www.itu.int/dms_pub/itu-t/rec/x/T-REC-X.520-200204-I!Cor1!PDF-E.pdf
BTW: Is the commonly used short name "fax" defined anywhere?
Norbert