First, I would like to thank you for writing this book. It has always been my biggest annoyance with Erlang, that there are too few books on the subject.
I haven't worked with Erlang in years, so forgive me if my knowledge seems outdated.
Recently I have been exposed to the principles of SOA. The first thing that struck me when I read about it, was how Erlang would be the perfect language to use for implementing a SOA solution.
I agree with Alain that basically, the whole philosophy of writing systems in Erlang is all about creating separate interacting services, and though we don't use the term "SOA", the book is really all about techniques for implementing a service oriented architecture.