Before hiring someone you would do yourself a big favor by running through some early low-fidelity prototyping. Start by sketching it out on stickynotes, get the flow down and get into the experience. You can move to a high-fidelity clickable prototype after a few iterations, possibly hiring a graphic designer to simply lay it out for you. Load this prototype on your iphone and show it off to real life possible customers for feedback. Listen and iterate. Now you may find that people don't care or you have a set of features (typically a few of them winning) that you can take into development. This becomes your specification and you can more easily find a programmer on oDesk or such. My advice is to do this work yourself or work very closely with a firm that specializes in this process. Good luck!