Digital extension the ericsson dialog 4224 operator system phone is a digital phone which only works when connected into a digital extension on an ericsson telephone system if you do not have an ericsson telephone system then this phone will not work there are a number of ericsson systems that this phone will work with including the ericsson md110 bc11 or bc12 as well as the ericsson mx one large lcd system phone the ericsson 4224 operator telephone has a very large 6 line