Rating: 

It's very heavy on the internals, classes, programming APIs, and state machines of their software, presumably, based on what they say, because they are trying to recruit more developers into the community.

That's fine, except for one thing: if we can't figure out how to be expert USERS of VOCAL, we don't have any hope of becoming developers. And this book is miserably void of any serious info on how to USE VOCAL.

For example, other than a few "./ua" lines, there is almost NO discussion of how to do anything from the Unix command line. Knowing how to use Dial Patterns, fundamental to any real learning, is buried in Appendix A. Coming up with a simple list of what-service-is-running-on-what-port in the all-in-one config should have been listed in a convenient table in the book; instead, I had to do lots of clicking through the GUI to figure out all that.

Figuring out how to place a variety of call between ./ua, Cisco ATA 186s, and the PSTN works to some extent, but leaves a lot of questions unanswered.