HCS-4886NX/50 Operator Unit is only used for intercom facility control, but cannot be used for conference discussion. Excellent immunity to RF interference from mobile phones. Channel selector and graphic display with backlighting, able to display characters from complex European languages or icon-based-scripts such as Chinese. Channel selection is automatically limited to the number of language channels available. The loudspeaker offers superior acoustics with minimal feedback for enhanced intelligibility. Under external mode, when an external call happens, operator listens to the content from the built-in loudspeaker or the earphone. By pressing the microphone On/Off button he talks to the caller (PTT mode), and the built-in loudspeaker is muted.