This seems to be a nice blend of physical and digital. Sketch on paper, make a photo, create a storyboard in the app.
Touch Application Prototypes (TAP). For iPhone and iPad, using Adobe FireworksMisc
Proto.io – Silly-fast mobile prototypingMisc
“Create fully-interactive high-fidelity prototypes in minutes that look and work exactly like your app should.”
check the details on proto.io