We specialize in rapid prototyping on mobile. We usually have a working prototype by the end of the first week of a project.
We've built over 50 apps, websites that serve millions of people, and 8-bit role-playing games. We have usually made something similar to what you're talking about.
We try our best to understand the goals behind a project so we can work fairly independently. Part of moving fast is being able to guess what the right decision will be most of the time.