Someone may have already brought this to light but I can't find it.
I recently found an app on the Nokia OVI store web site for an application for my Nokia smartphone that works out the Depth of Field. It caters for various types of camera (APS-C, DX, Full frame etc). It will save me carrying around the printed pieces of paper with the DoF charts printed on it. The web site is http://store.ovi.com/ . The application is called "Phototools".