iPhone Application to connect to existing booking system

We have a requirement to create an iPhone application to query and display information from our existing online booking system; the existing booking system is written using Microsoft .Net / C# and the backend database is Microsoft SQL Server. The app will consist of approximately 13 screens and will need to display data (TableViews) as well as images (ImageViews) with a login screen for secure access. The app will not need to store data and the app will only be available whilst the user is online. We will provide mockup screens and will create the web service calls, which will be documented for each screen. The app will be written using Monotouch (C#) or Objective C (please specify) and should be compatible with iOS 4 and above (including iOS 6 when available). Note that it will be the developers responsibility to ensure that the app meets Apple's guidelines and no third party controls or code should be used unless agreed beforehand.