Cisco Headset Adapter for 2.5mm headsets Converts a standard 2.5mm handsfree into Cisco RJ-9 modular plug headset. Compatible with Cisco 7945, 7965, 7975 as well as with older Cisco IP phones. Allows to use the same headset at the office and while you out of the office. Connects into the headset jack at the back of Cisco 7900 IP Phone.