I used this book to create a web site for WAP devices, during a university project.
Considering that this was my first WAP site, it looks very professional, and I think that Chris Tull deserve this success.
WAP 2.0 Development is a great book for its simplicity in explaining the arguments.
The only problem with this book is that it refers only to Windows systems (like Access DBMS) and it explains interaction between WML and APS instead of PHP, which is a very spread language of scripting server-side.
I suggest to buy this book if you don't have any programming skill in WML; if you know basic WML try to buy a more complete book on this argument.