If i remember correctly plantronics has three different base units connecting, at the handst jack, thru a splitter at, and the last with some type of xhook lifting device. There was several different base/amplifiers and they have many diferent headsets that could be used with them. By the time i was done configuring it, i was doing it only as a courtesy for my customer.Plantronics was very helpful if you need to call them print the product sheet first it will be helpful to see what they are refering to. good luck