The ericsson extra key panel is an add on unit designed to attach to the ericsson dialog range of telephones not all the dialog phones have the capability of attaching an expansion key panel as not all of the models have the slots ericsson phone compatibility the ericsson dialog phones that are compatible with the extra key panel unit are the ericsson dialog 4222 ndash 1 extra key panel only ericsson dialog 4223 ndash 1 4 extra key panels ericsson dialog 4224 ndash 1 4 extra key panel