Recall, Esri has a free ArcGIS client available for iPhone (iOS). The app has been recently updated with even more functionality. ArcGIS for iOS extends the reach of your GIS from the office to the mobile Web. It includes an application for Apple iPhone, iPod Touch, and iPad devices
New in V 1.5
Data Collection and Editing
– Use your GPS or the map to collect and update GIS data
-Attach photos and movies to what you collect
See also the ArcGIS API for iOS – Using the ArcGIS API for iOS, you can develop focused applications for iOS devices that can be deployed within your enterprise or to the public