iPhone Mobile Safari User Agent Faking
You can import this XML file into your User Agent Switcher plugin for Firefox so you can view and test the mobile or iPhone version of a site. The user agent string is the one described in this tip. (After installing User Agent Switcher, restart Firefox and go to Tools • User Agent Switcher • Options and click "Import.")
Also of note is that the iPhone Simulator (part of the iPhone SDK from Apple) does include Mobile Safari and can actually navigate to your local development site (e.g. localhost:3000 or any other server running on your computer), not to mention the Web at large.