I have a pre-existing desktop application that draws its information from a Microsoft SQL Server. The desktop application is written in C#/ASP/.NET.
I'd like to take this same data and present it in an iPhone application. What would be the best way to obtain and present the data?
I would recommend writing a web service that exposes the data and then interfacing with this from the iPhone across the network.
Calling web services and making HTTP calls is very easy on the iPhone.
Do you assume your iPhone application will have network access? If so I would go the webservice route as already mentioned. If it's a small database that you want available on the iPhone with out the need to access the internet to retrieve data you could look at converting the SQL Server database into a SQLite database and packaging it with your app.