Over the past several weeks, I've encountered Balsamiq Mocups as a tool for creating wireframes of iPhone apps. This week, I downloaded a trial version to do some mock ups of my own. Balsamiq offers a fully functional 7 day trial that requires a license to save designs after the trial period is complete.
So far I have been impressed with the interface and ease at which I have been able to put together some simple workflow mock ups for apps. There's not a ton of iPhone specific control types available, but the set provided works pretty well for simple productivity type apps. It would be nice to see some more items added to the native set of templates. I'm sure there are custom ones available, but it'd be nice to have some more templates just built in. There's also currently no iPad templates. This is a gap in the toolset for iOS. Its becoming much more common to have universal apps that incorporate iPad views. I've seen some indicators that the Balsamiq folks are considering adding iPad... but with the release the second generation already...the absence of iPad templates is making the tool feel obsolete.
It's a solid start to providing a tool for doing quick wireframe of iPhone apps. Hopefully there's more templates coming soon that make the wireframing for mobile even quicker.