Information Week's Nick Hoover has written a very length, super informative and practical story on what you need to know as you get ready to switch to VoIP in your business.
What I like about his story is how clear and concise the language is, and how he has provided real world examples of how businesses that were early adopter's overcame the challenges of an emerging technology.
Give it a read if your company is getting ready to migrate to VoIP!