I'm working with a legacy app with a deployment target of 3.0. I have a crash being reported on iOS 3.1.3 for iPhone. In xcode 4 the only 3.x simulator I see listed is iPad 3.2
How do I test iOS 3.1.3 for iPhone?
See Install xCode 3.2.3 w/ iPhone SDK 4, get "Base SDK missing", can't see other SDKs for an extended discussion of this topic. Also, links to older Xcode and iOS SDK versions can be found at http://chris-fletcher.com/2010/08/28/howto-install-iphone-sdk-2-0-3-1-for-xcode-3-2/.
Buy a used iPhone or iPod Touch that has 3.1.3 installed and don't update the iOS on it. I have a 3G with 313, no cell service and just use it for testing on wifi. This is also useful to see check what the performance is like on a slower phone.
However, many 3.1.3 crashes are caused by using a 4.0 API call or object that is only in 4.0. You can find those problems on the 3.2 simulator.