Jakob Nielsen offers insightful information on making a great mobile phone application: http://www.useit.com/alertbox/mobile-apps-initial-use.html
Most mobile applications are used only intermittently, so they must be especially easy during initial use. In particular, upfront registration shouldn’t be required before users experience an app’s benefits.
Among the findings and recommendations:
- Users can’t touch as precisely as they can click, so the number of manipulable graphical objects should be much smaller (so that each one can be much bigger).
- On mobile devices, applications are easier to use than websites.
- People install many more apps than they actually use, so to measure your app’s success, you must measure actual use.
- Mobile mainly equals intermittent use.
- Avoid making users pass through a registration screen as the first step.