Design a complete Voice over IP (VoIP) or traditional PBX system with Asterisk, even if you have only basic telecommunications knowledge. This bestselling guide makes it easy, with a detailed roadmap that shows you how to install and configure this open source software, whether you're upgrading your existing phone system or starting from scratch.Ideal for Linux administrators, developers, and power users, this updated edition shows you how to write a basic dialplan step-by-step, and brings you up to speed on the features in Asterisk 11, the latest long-term support release from Digium. You'll quickly gain working knowledge to build a simple yet inclusive system.Integrate Asterisk with analog, VoIP, and digital telephony systemsBuild an interactive dialplan, using best practices for more advanced featuresDelve into voicemail options, such as storing messages in a databaseConnect to external services including Google Talk, XMPP, and calendarsIncorporate Asterisk features and functions into a relational database to facilitate information sharingLearn how to use Asterisk's security, call routing, and faxing featuresMonitor and control your system with the Asterisk Manager Interface (AMI)Plan for expansion by learning tools for building distributed systems
Very good source on how to get started with Asterisk and get a running and well maintainable PBX. The book is completely fine for latest version of Asterisk (14 at the time) and I didn't meet any issues due to the fact that it was written for 11th version of Asterisk.
Note that this is a definitive guide and not an end-to-end "tutorial" book that will teach you step-by-step what you want to do with your PBX.
Before getting started with the book you need to have a clear goal what you'll do with your PBX and start achieving your goals one by one. E.g - get the PBX running, get a DB integrated, install SIP devices, add extensions for internal communication and test that it works. From there on you can iterate and add outbound calls, inbound calls but you'll require trunks and DIDs which might be more or less depending on your business goals here.
Either way, I recommend this book big time, cause sinceriously this is the only Asterisk book resource that's almost up-to-date. Everything else I could gather as info was from official Asterisk docs and https://www.voip-info.org/wiki/view/A... (and its many pages for Asterisk with examples). Don't get me wrong, all these resources must be used in combination to get the most out of Asterisk.