The invention comprises a variety of unique adapters for use with modular plug telephones. The adapters permit multiple handsets or multiple telephones or any combination of both to be connected with a single telephone wall jack. The adapters comprise multiple jacks and plugs with suitable electric connections...http://www.google.com.au/patents/US4362905?utm_source=gb-gplus-sharePatent US4362905 - Universal adapters for modular plug telephones
