Many of the SimpleViewer-Pro features (such as the Back Button) are available in the Flash Player version only (and not in the Mobile Player version).
The Mobile Player has a much smaller feature set than the Flash Player. Configuration options supported by the Mobile Player can be found here.
SimpleViewer is primarily a Flash image viewer and the Mobile Player was designed as a fallback for mobile devices which do not support Adobe Flash so that all visitors to a site will be able to view all images within the gallery.
If you are looking for a more fully-featured solution for mobile devices, you might like to take a look at another one of our products: Juicebox.
More more information on the differences between SimpleViewer and Juicebox (and details on how SimpleViewer-Pro users can get a discount off the cost of Juicebox-Pro) can be found in this SimpleViewer news article.