A method for calculating zero-crossing reference sequences for the data detection of a sequence of zero crossings }i}) of a received signal is disclosed. When a subscriber receives a telephone call, a determination is made as to whether the call should be routed to the voice mail system. The bus bar is made of an electrically conductive material, while mounting unit is made of an electrically non-conductive material, such as a plastic, thereby providing a \u201ctouch safe\u201d enclosure.