I've always felt that it is critical to ensure that we train each other on how we want to be treated. That being said, we should use discipline and respect for order to determine the standard operating procedure to guide our responses to situations. So, when our colleagues telephones about an "important" issue and we know that our commitments dictate that we focus on the activity, we simply say "I'm a little busy now can we discuss this tomorrow?". Please be sure to write "Call John" in the appropriate "Things to Do" list.
Failure to do so will create one very angry John!