The M12E Vista adapter is the premium universal adapter that connects your headset to your phone & can be used with a wide range of Plantronics headsets. It is compatible with the majority of business telephones & features Plantronics Call Clarity & Sound Guard Plus technologies, which enhance the quality of the call & ensures that what the user hears is kept at a comfortable level. The Vista has a headset/handset switch, full volume controls & mute button. Unlike the standard M12, The M12E has a switch on the side, which switches the wire configurations, thereby making it compatible with different phones. Only used on non-standard wire configurations.