You don't mention what you use so I'll go with CUCM, you need to provide that information when posting.
You can just go to the device and uncheck the DND option, if the softkey is not showing, check the softkey template or feature policy depending on phone model.
HTH
java
if this helps, please rate
www.cisco.com/go/pdihelpdesk
HTH
java
if this helps, please rate