Great use for call center / telephone marketing trainings. Now both users can simultanous listening / talking into one conversation via this adapter. Mute button control with indicator when on to avoid accidental talk into conversation. Lightweight and durable and provide great sound quality. Can plug either into handset port or headset port. ( SEE COMPATIBLE LIST ). Plug and play : Can plug either into handset port or RJ9 headset port ( SEE COMPATIBLE LIST ). Allows the use of two headsets on one telephone, plug and play. This headset splitter will give you two more ports to headset or handset corded plug in, it helps with training and also acts as an extension cord. SEE COMPATIBLE PHONE LIST IN DESCRIPTION BEFORE MAKE PURCHASE.