How does “Open With” some app in iPhone work?

Question

As far as I know, from iOS SDK 3.2, file type handling is added and an iOS application can associate itself with some file type so that other applications can open this kind

Answer 1

Sndbox implemented over standard unix permissions control. All applications are stored in folders with unique name (actually, GUIDs), however owner for them is the same mobile:mobile. So it looks like they just sends full file path to application which opens the corresponding file.