[Unity3d] C++ dll for iPhone and XBox 360

#if UNITY_IPHONE || UNITY_XBOX360

   // On iOS and Xbox 360 plugins are statically linked into
   // the executable, so we have to use __Internal as the
   // library name.
   [DllImport ("__Internal")]

   #else

   // Other platforms load plugins dynamically, so pass the name
   // of the plugin's dynamic library.
   [DllImport ("PluginName")]

   #endif

iOS and X-Box use dll as a static library. So, you should use "__internal" when importing.