When this device is "on hook", the speech circuit is disabled & the ringing circuit is connected
The ring lead portion of the tip/ring wireline pair is connected to a controlled ... 
circuit device coupled to said telephone line, to enable operation of a limited ... 
for an on-hook condition of a telecommunication circuit device... [DOC] [TLE] Patent US6697472 - System and method therefor of preventing ... [PAR] Feb 24, 2004 ...