I do not have call waiting on my phone because I think it's rude to ask someone to hold so that I can take another call and when I'm working I don't answer the phone. When I'm working I don't want to stop what I'm doing because it's a waste of time having to go back and figure out where I left off and when I reach a convenient place to stop, I turn of the clock and check voice mail and return calls.
My message isn't long and drawn out, it's short and to the point thanking the caller for calling, telling them who they've reached and when they'll get a call back. I've actually received compliments from callers on the professionalism of my voice mail; one person told me that they thought it was great customer service.
This voice mail protocol is a tip I learned in a time management course.
Everyone has their preferred way of doing things, if we were all the same, the world would be a pretty dull place