Settings > Receiver and Headset > Headset Type

Headset Type
If a headset is connected, the headset type used must be configured.
Cable headset / wired headset: Selects the cable-connected headset type.
DHSG headset: Selects the wireless headset type with a DHSG interface.
 
Proceed as follows:
Using COMfortel Set (page Settings/functions > Headset, list field Type of headset)
Using the telephone (menu settings > headset > headset type)

COMfortel 2600 - Firmware V2.2 - COMfortel Set V3.16 - Advanced Information V10 02/2019