Hit the More button then,
Hit Away button
until the Do Not Disturb banner on the phone goes away. Let the announcement complete after every press. If you hit the button in rapid succession it will cause the phone/ line to get out of sync.
Then dial *79<send>
You should be out of DND.
To enter DND mode, use the Away button once...same as above, let announcements complete before pressing again
Do not use the DND button found in the Settings menu, this will cause the Phone and the Line to get out of sync.
If you have any questions, please call the Help Desk at x6000.