When this device is "on hook", the speech circuit is disabled & the ringing circuit is connected
... the band of the speech currents, it is necessary to disable the ringing 
circuit of... [DOC] [TLE] Cisco IOS Voice Troubleshooting and Monitoring Guide, Release ... [PAR] Feb 12, 2014 ... Two-wire circuits connect to analog telephone or fax devices, and four-wire 
circuits ...