This cable from Jabra allows supervisors, quality assurance and staff trainers to split an existing QD headset connection, allowing the connection of a second headset with both headsets able to speak.
Features single QD connector at one end, and two QD connectors at the other end. Jabra recommends the use of an amplifier with this cable, even on phones with a direct connect headset port. The Jabra GN8000 MPA amplifier is recommend.
This cable is also available in a "observation only" version for situations where you want the second headset user to be able to listen only, and not speak.