Audicom Telephone Training Adapter Y Splitter with RJ9/RJ12 Plug Connections for Corded Headset or Handset for Aastra Shoretel Cisco E20 Polycom 335 VVX400 Digium D40 D70 Altigen IP Phones(YTRJ-STAC) Can plug either into handset port or headset port.Allows the use of two headsets on one telephone.The headsets must be compatible with the telephone models listed in the product description. Handset or Headset Splitter, Complete with RJ9 Great use for call center / telephone marketing trainings Easy setup, plug and play ONLY WORKS FOR SOME SPECIFIC PHONES. PLEASE SEE COMPATIBLE PHONE MODELS LISTED IN DESCRIPTION BELOW