I just read a post from Mark Deakin about business communication etiquette. He has worked with The Finishing Academy to come up with some guidelines.

At first I wasnt sure about this, but then thought about how annoyed I get when people write an email when they could have just picked up the phone, or even worse when what could have been a 2 minute phone call turns into a 37 thread email, and even worse than that when the tone of an email is read incorrectly and then it becomes a 135 thread email of abuse and rudeness

Rant over...now I am going to pick up the phone!