Isn't it for work?
Someone else mentioned tutorials, you should try those first as they will help you begin working with wxwidgets.
I do not think this book is freely available as an ebook.
You might be able to get it used for a reasonable price... Though according to amazon, it hasn't been released yet.
If you need it for "work" though, won't they cover the cost of the book? If your work is for an open source project I might be willing to help you get a copy of the book.
See, I am planning to buy it as soon as it is released, if you want, I could send you the book after I have read it. That might be like six months or more from now though. If you don't mind waiting and would like to do that you can email me: jacob \|. a t -)/ quant.us