The aastra extra key panel is an add on unit designed to attach to the aastra 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 aastra phone compatibility the aastra dialog phones that are compatible with the extra key panel unit are the dialog 4222 ndash 1 extra key panel only dialog 4223 ndash 1 4 extra key panels dialog 4224 ndash 1 4 extra key panels dialog 4225 ndash 1 4 extra key