taken directly from the ESRI website:

"ArcGIS Apps for SmartPhones extends the reach of your GIS from the office to the field. It includes a free application that you can download from the Apple App Store or Windows Marketplace. Both Apps include a developer focused API that you can leverage to build your own custom Windows Phone or iOS applications.

Application Highlights
  • Find and share maps from ArcGIS Online.
  • Use tools to search, identify, measure, and query.
  • Collect and update GIS features and attributes."