Hello!
I've downloaded the latest SDK from developer.apple.com and can only pick 3.2 or 4.1 from Project > Properties > Base SDK.
My iPhone is 4.1
My client have iPhone 3.x
You feel the problem...
How can I debug for iOS 3.x in xcode with the 4.1 SDK installed?
Actually that's a very frequent question (was lazy, only linked one).
Short version: you need to set your Base SDK to the highest SDK version you've got and your project's Deployment Target to the lowest version you like to support, e.g. 3.0. This means, the Deployment Target specifies the oldest version your app should be able to run on. But beware, this setting does not prevent you from accidentially calling, say, methods available since 4.0 on an 3.0 iPhone and thus causing a method missing exception.
I understand that, DarkDust.
But for example, when my client runt the application a few labels isn't visible on his device, but it is on mine.
On my device everything is fine, but on his, it isn't.
How can I simulate 3.x on my device so I can fix the problems?
This isn't possible have I come to understand.
You have to buy a old iPhone 3.x.
If you want my opinion on this, then I think this is horrible, frustrating and completely not understandable.