Helpful Asterisk resources
Two years ago I bought Asterisk: The Future of Telephony
. The book soon became a very important resource for me, and I strongly recommend it to everybody who want to learn the basics of Asterisk. Now you can check it out online, O’Reilly Media have published the entire book free of charge!
Another very good resource of Asterisk knowledge is the newly published trixbox CE 2.6 written by Kerry Garrison. As one of the reviewers I have spent a couple of hours 
with this book, and whether you are a dedicated trixbox fan or not, it’s well worth both the price and the time. The book is written for those who want to learn how to install and configure either trixbox CE systems or Asterisk-based PBX systems, without struggling with confusing configuration files and cryptic scripts. It is ideal for any user wishing to set up a telephony system for small business usage. No previous knowledge of trixbox or networking is required, although some basic knowledge of PBX and Linux would be an advantage.