How do I remove the need for dialing 9 to get out to an external number? For example; if I start dialing 404-###-##### it asks if I want to disable/enable DND.

I'm assuming you're talking about they pick up the handset and then begin dialing the number? If you do this, then you will take away a lot of the internal function of the phone. Meaning they can't dial extensions or do other features. The one way I know is to hotline the phone to the trunk group. That way when they go off hook it automatically acts as if they pressed 9 and then they can just dial the number.