... , so you just need press a button to achieve a variety of functions, such as the call outside, call extension, ... ringer volume) can be adjusted quickly by Volume control key. 8. Conference key (CONF), you can quickly convened a meeting, which can ... line. 11. Check ( CHECK ), remove ( CLEAR ): system programming, key programming. 12. Earphone key ( EAR ): switching to a headset answer mode, handle off ...