You can use 'Cloud Voice Group (or Site) Intercept' to intercept calls to a specific user or site with a message and alternative routing options.
Say you're still getting calls to a line that you no longer use; you can play a message to your callers like: 'This number is no longer in service. To talk to an operator, press 0'.
Or maybe no-one can get into the office because of floods or some other disaster; you can use this feature to quickly get a message to callers telling them that your office is closed or whatever.
You won't be able to make any outgoing calls from a line with an intercept on it, with the exception of 999 calls.
Note: You may need Adobe Reader to view PDF documents.