Are you asking about running the standard Salesforce Chatter Mobile application in the iPhone simulator, or developing an iOS application that integrates with Chatter?
As far as I know, you can not run applications in the simulator without their source code or developer signing, so that's not really an option. Developing Chatter integrated apps is pretty straightforward when using the iOS toolkit.
Are you asking about running the standard Salesforce Chatter Mobile application in the iPhone simulator, or developing an iOS application that integrates with Chatter?
As far as I know, you can not run applications in the simulator without their source code or developer signing, so that's not really an option. Developing Chatter integrated apps is pretty straightforward when using the iOS toolkit.