I started using an Adobe Air application today called “Balsamiq Mock Ups”.
Up to now I have been using Powerpoint 2007 which does an adequate job in layong out Mock-up screens for co-workers and clients.
I have an iPhone for a few months now, a 16GB one with 3G.
The iPhone is mostly brilliant but does fall down badly in a few important areas, like battery life and text messaging.
Anyhow it is mostly brilliant, and a joy to use for surfing the web and reading email.