Digital extension the ericsson dialog 4220 lite telephone is a digital telephone that will work on any digital extension on an ericsson telephone system the dialogue range is compatible with the ericsson mx one md110 bc12 and md110 bc11 telephone systems however if you are unsure whether your ericsson system is one of these just check the model of phones you are using at the moment if it is an ericsson dialog then you will be fine cost effective system phone the ericsson