As a change leader you need to make decisions about who you must communicate with, what needs to be communicated, when you will communicate and how you will do it. We will take a look at each of these in turn.
Who?
Managers sometimes have a tendency to communicate about change on a "need to know basis". However, effective change leaders recognize that almost any change will have effects on most people in an organization, no matter how removed they are from the change.
The basic rule of thumb is that communication should take place directly between the manager and employees when employees NEED TO KNOW OR WANT TO KNOW.
Except for situations that involve confidentiality, even those who are indirectly affected will likely want to know what is going on, and how it may affect them. This applies to your own staff, and those organizations that are related to you (ie. other branches within a division or department, client organizations, etc).
You are better off over-including people in your communication, than leaving people out.