Home → PressONE Customer KnowledgeBase → Cisco 7940/7960 User Manual → To disable Do Not Disturb:
• Press the DND softkey or lift the handset, dial *04 and hang up. The "Do not disturb is active" message will disappear.
You can record a special voicemail greeting that callers will hear when you have DND active and they are routed to voicemail.