The book is a good introduction to PHP web services, cURL and DOM. It goes into details of building a web service from scratch. That is good for understanding, but I would much rather use a framework from WSO2 or Zend.
Book has a lot of examples. Though the examples have a few problems
1. Very basic sample programs for RESTful server.
2. A lot of code is printed, but with very little explanation.
3. Code explanation does not offer more than what you would get by reading the code itself. No options or pitfalls are described.
4. Printed code formatting is awful. Statements wrap around, instead of line breaks and indentation. Random words are highlighted. Bold words have no connection to the concept being explained. For example, frequently (but not always) functions have plain "return;" highlighted.
All that makes the book hard to read.
Before buying the book, check websites for WSO2, Zend, Flickr and Yahoo. They have good documentation and tutorials.