Administration Guide
Page 150
...you must unlock the network setup options before plugging it loses contact with certain types of these statistics. 9-10 Cisco Unified IP Phone 6921, 6941, 6945, and 6961 Administration Guide for information about displaying these statistics should directly connect to a switch port. ...digital cell phones using G.729, calls between the phone and another IP phone through the connection, the network card can be destroyed. Codec mismatch between an IP phone and a digital cellular phone will not work. When using the G.729 protocol. Dual-Tone Multi-Frequency (DTMF) delay...
...you must unlock the network setup options before plugging it loses contact with certain types of these statistics. 9-10 Cisco Unified IP Phone 6921, 6941, 6945, and 6961 Administration Guide for information about displaying these statistics should directly connect to a switch port. ...digital cell phones using G.729, calls between the phone and another IP phone through the connection, the network card can be destroyed. Codec mismatch between an IP phone and a digital cellular phone will not work. When using the G.729 protocol. Dual-Tone Multi-Frequency (DTMF) delay...