A few people have asked us about developing apps for the iPhone, but on the whole we don't think you need one (and not just because we don't develop them). Obviously there are plenty of useful and popular apps on the iPhone and other smartphones, like games and gadgets that are developed specifically for mobile use. (iPhone 4 image courtesy of Apple).
But if you've already got a website and think you should have an iPhone application to go with it, think carefully about what you really need. The main reason to have an iPhone app is so that your customers can use it while they're offline - otherwise you're probably better off customising your existing website and avoiding the investment in new technology, and the risk that your app isn't accepted by the iTunes store.
Instead, get your website developers to make sure your website works properly on mobile browsers. You can even create a stripped-down version of your website with fewer functions, to give mobile users a quick and simple resource. For example, we use Campaign Monitor for our email marketing and where their normal website allows you to manage subscribers and send campaigns, the mobile version simply shows a basic login screen followed by mini reports on your campaigns, which is just what you want if you're having a quick look on your mobile.