eRider Starter Kit. by Teresa Crawford & the Tactical Technology Collective Lots of information about developing a technology plan, and managing IT projects.
Asterisk: The Future of Telephony Jared Smith et. al.
Also available as an open source .pdf book as a free download. I don’t know if this is what the Asterisk Documentation Project was supposed to become, but this is an outstanding book providing both a general overview of Asterisk and VoIP generally, and specifics related to hardware issues and the “dial plan”…argueably the most confusing and least documented aspect of Asterisk. Highly Recommended. Don’t just download it, buy the book.