There have been many complaints that devices were unable to progress past the “Slide to Upgrade” screen when moving to the latest version of iOS.
Apples solution is not great. It is telling users to wipe their device and pray to Steve Jobs that you made a backup.
Instructions posted to the Apple support site advised users to perform a factory reset on the frozen iThing and then restore from a previous backup.
Apple’s suggested clean install procedure does work, but it can take you several goes.
The issue appeared to be largely relegated to devices running iOS 7 skipping over to iOS 9, Apple would not confirm if that was in fact the case.
In fact the only work around you can be sure of is to hit your iPhone with a hammer and buy something less problematic, and cheaper.