If you are a radio amateur with an iPhone there are already a wide range of apps out there, some more useful than others. Mark Turner's commercial presence on line is called KramStuff and he is pushing two of his ham apps at the moment. Ham Dashboard sounds like another of those things to clutter the taskbar of your browser, but it is in fact a neat application that shows a searchable list of nearby repeaters in the UK, along with details of input and output frequencies, a map, and a handy bearing arrow for each repeater. Reading between the lines I think future versions will have more features. It comes with a database of repeaters which can be added to or edited, and it has a handy default button for if/when you mess everything up.
Just as useful is Ham Square it is a simple and free app that shows your current Maidenhead Locator, i.e. your "square". There are already a few apps like this and I already have one in my old PDA that does this plus it gives you all the other locators that you might need, but hey this one is free.
Personally I don't have an iPhone yet but if I did I am sure I would be downloading these from the appstore.
Ham Square download Free
Ham Dashboard download £1.70 at time of press