You should consider switching this to a freelance project instead of a contest, as even though you are not asking for the full UI at this stage, your prize fund is far too low to receive entries from professional UI designers.

If you were to switch it to the quote based project on here, where by you receive quotes and supporting portfolios from designers you will find you attract the level of professional designer I assume you are searching for.

And from there you can immediately begin working with the one you select.

I can safely say I will not be the only professional UI designer on here to have this view, so I thought I'd just suggest the alternative method for you to consider. Good luck in your search.

What resolution do you expect to have? - iPhone4 or iPhone5?

Hello,

Are you able to clarify what the difference between this and your other job is?