Create an App

I want created an App that is able to work with Android 2.2. Tablet pc's, Android 2.3, Iphone, Ipad and Blackberry. The App, should allow ; 1. Users to post ad's and make money from people offering them work. 2. App, should have messenger service similar to BBM , where users when registered with the App, will have a unique membership id, where they can add other members and communicate with eachother. We need companies to pitch who are confident and experienced in developing these types of Apps and are confident they can complete within a limited time.