Thanks for the post and yes I'm hoping we'll have a more substantial iOS app in time.
A few things are holding us back -- (1) the need to really simplify the interface of whatever app we put together, (2) the need to actually program it, and (3) the fact that it isn't a priority from the business side of things: our big challenge is less getting technical work done than figuring out how to let people know about us.
In about a month we'll be shifting to a new version of the site that I hope will be a meaningful step up in the usability department, not just in terms of making it easier to use some of what are now premium features, but also through the addition of a structured testing component to help people identify what they don't know but really should. We're also putting work into a simplified interface that should work better on smaller screens like the iPad and iPhone, and make the site more useful on small screens and tablets.
Once that is done we'll be in a better position to see how to translate things to iOS or Android devices. In the meantime, you CAN open the mp3 files on the site directly in Safari if you want if you open them from the right-hand menu in every lesson.
* we'll automatically turn your links into html.