GN/Jabra Cisco HHC Adapter enables remote Headset Hookswitch Control (HHC) with GN/Jabra wireless headsets(ie. GN 9350 or GN 9120),and the latest generation of Cisco Unified IP phones. This means that users can answer and end calls up to 300 ft. away from their desks. The seamless integration of handset and headset allows users to benefit from enhanced mobility and the ability to multitask while on a call. The wireless freedom improves work efficiency and ergonomics througout the day. The GN Netcom HHC Adapter is a plug-and-play solution that converts from the HHC standard used in Cisco phones to the DHSG standard used in Jabra headsets – and vice versa. Handset-Headset compatibility

GN/Jabra HHC Adapter is compatible with these Cisco IP Phones: 7942G, 7945G, 7962G, 7965G and 7975G. Cisco Unified IP Phone release 8.3(3) will enable the HHC functionality.   Do not order this adapter if your phone is not listed

For more information.  See GN Cisco HHC explained , GN HHC adapter datasheet and Cisco IP Compatibility Chart