The situation has changed recently for iphones. Parts are icloud locked now. While the part serial is registered to an icloud locked iphone. Any phone with those parts will refuse to work entirely until the part is either removed or the part is unlinked from the owners account.

This would be the way to go if on the flip side any part that was not iCloud locked could be paired without hassles. Phone stolen/lost/etc? Parts unusable. Phone iCloud unlocked? Parts free for use. Of course this depends on mitigating various ways thieves can iCloud unlock stolen phones..I think the current method is snatching the phone while it's in use and iCloud unlocking it? However that doesn't make much sense since I assume you need some sort of password to do so even if the phone is physically unlocked?

Source? What message does iOS show?