This book is the most complete book I've seen on WAP -- it covers alot of topics that others books don't, such as WTA and Push. It also provides a great background on wireless and why WAP was developed (and why).
Most of all, the book teaches how to write content for all phones, not just a single one. This is difficult, as the book keeps pointing out, but it guides you through all the gotchas. The UI chapter is a big help too.
I highly recommend the book to anyone who wants to write great WAP content.