The DND button controls the Do Not Disturb function. When you turn on DND, your LIVE phone will not accept any incoming calls. This gives you a way to temporarily refuse incoming calls without stopping your LIVE software. If another LIVE user places a call to your LIVE phone, they will get a "busy signal". You can still place outgoing calls, and use other LIVE features, while Do Not Disturb is activated. Click here for more information.