I've done some design I have about a 5-'page' application to have developed for the iPhone. There are about 42 fields in the application. Only 8 are for entry, 4 are settings, and the rest are all simple calculations (okay, one a payment calculation).
I have sample iPhone pages and field calculations so requirements gathering will not be a long process. I'm sure there may be some things on the look that will have to be discussed but again, the app is not terrible complex. Currently is it an Excel spreadsheet.
There is a second project as well to add functionality to base app and I will want same app ported to Droid, Blackberry, and Windows platforms too.