These applications suffer from the worst usability since the days of the teletype. Let's consider the deficiencies of WAP apps with typical desktop applications. Yes, the screen is smaller. Yes, one of them can go wherever you do. OK, now that those are out of the way, let's dig a little deeper.
Usability is about more than screen size or bitmapped buttons.
It is about how easily a user can get the job done. It is about the system helping, instead of impeding, users' interactions. I am not speaking specifically about Windows, Macintosh, or X desktops, but rather, the modes of user interaction employed by those popular environments. Of course, it's easy to point to the worst offenders against each of these principles. In the language of patterns, a solution balances forces in a context to produce a resulting context.