Even if the basic concepts are still the same, many things changed since the first SER-related book written by Flavio E. Goncalves. A successor has been requested many times on ML and IRC. And, as announced last week on OpenSIPS' mailinglist and website, now it is finally available. Packt Publishing asked me whether I'd like to read and review it: of course I do!
If you are about to make your first steps with OpenSIPS: get this book. Immediately. I've read the OpenSER-related one as soon as it has been released - and I wished there was available such a book once I started working with SER/OpenSER.
If you are still unsure please stay tuned: a hardcopy is on it's way to my office. I'll provide you with an in-depth honest review - hopefully within the next two weeks