We recently launched our PC headset adapter with phone jack, but we’ve had customers wanting to use their phone headsets with their office corded phone. So we just launched a 2.5mm to RJ9/RJ1/RJ22 (not RJ11) headset adapter for Nortel, Aastra, and most corded phones, as well as a 2.5mm to RJ9 headset adapter for Cisco, Avaya, and Polycom phones.
Note that RJ9, RJ10, and RJ22 phone handset and headset plugs have four connectors, not six like RJ11 plugs. RJ11 is only used to plug the phone into the wall.
Be sure to see which of our Headset Buddy adapters fits your specific model of phone because thev have different wiring.