Before submitting a bug report, please check the iOS Troubleshooting page, where you will find solutions to common crashes and other problems.
If your application crashes in the Xcode debugger then you can add valuable information to your bug report as follows:-
If your application crashes on the iOS device then you should retrieve the crash report as described here on Apple’s website. Please attach the crash report, your built application and console log to your bug report before submitting.
Is something described here not working as you expect it to? It might be a Known Issue. Please check with the Issue Tracker at issuetracker.unity3d.com.