My opinion would be that most of the advanced functions you click once and then back to the main number pad, eg normally you do a calculation then hit "sin()" or ^x or whatever.

So I would have thought you treat the second screen like a symbol screen. Numbers on one page, switch for the less common functions, as soon as you click one it flicks back to the numbers pad? Check out the screenshot I sent before of the Mac calculator, I think it does a very good job of splitting the buttons into common/less common and the two groups of digits would make two very nice screens that you could swipe left/right to?

Just a thought?