It seems that only my 301 ext. can switch to night mode. I try pressing 818 from any other extension and just get a busy signal. How do I set up these other extensions so that they can also use programmable day/night mode operation changes

it is a Class of Service issue, It is supposed to work tat way under normal circumstances. that way you don't have everyone switching modes randomly. You will need to get the COS changed for the extensions you want to change the night mode.