Mehta instructs about coding for cellphones, covering topics ranging from GUI development to accessing a database server.
If you already have experience writing GUIs for desktop or web applications, then the GUI part of the text should be dead simple. Of necessity, there is a severely constrained graphic environment on the cellphone. It is good, in the sense that you don't have much to learn, and almost certainly, the complexity of your GUI should be low. Of course, the tradeoff is this very constraint. You are very limited in the images and widgets you can display. Back to basics, one might say.
Hopefully, you'd have dealt with database schema and designs in other contexts. The text's coverage of this is somewhat abbreviated. Enough is given for the book's main example to be nontrivial. But this is not a database book; just keep it in mind.
Payment is a no-doubt germane issue for some developers. The text describes how eBay's Paypal can be used for billing purposes.
The other interesting topic in the book is a brief explanation of Interactive Voice Response systems. Since after all, the user can talk into her cellphone. Just as for databases, IVRs have their own complexity, hinted at here.