Package Included: 1 x 4-Pin RJ9 Crystal Headset 1 x Headset Adapter NOTE: If you can not hear or others can not hear you, please try to adjust the adapter. How to use: 1, Plug the adapter (the headset comes with it) into the phone RJ9 port, then plug the headset into the adapter. 2, There is a line sequence switch on the adapter(it has the numbers 1 - 8). Note: Make sure to try each of the 8 "Channels"**until you find the one where you can hear them and they can hear you. Note: 1,Compatible with the most headset-ready landline telephones or devices that support 4 pin rj9 plug headset. 2,this headset just can be compatible for professional call center phone, may not be compatible for cordless phone , please make sure the port before order. 3,use the headset with adapter, can be compatible more different call center phones. the adapter have 8 modes, try to test every kinds to your device.4,this headset just can be compatible for cord phone. Not for cordless phone.