Activation lock is set to become an issue for many people, I’ve read article about refurbishing and trade in programs running into massive issues with physically perfect phones
When the father in law got his first iPhone 4 (which he still uses) he went it alone and fumbled through setting it up… problem is he ended up with an @me.com account which is his iCloud account on that device and of course he doesn’t remember his password… and the recovery email is an account he no longer has… and he set a custom question to unlock it… the question is “Custom Question?” which of course he has NFI what it is.
Long story short, a call to Apple confirms that unless he can find proof of purchase he’s completely boned (and of course he can’t find anything from back then). So while he can keep using this phone in it’s current form he can’t do much else with it in the future.
On the upside he’s planning a new iPhone this year so will just have to start fresh with that phone and a new iCloud account. (which also means he has near ZERO interest in attempting to track down proof of purchase which is sad since the phone has spent it’s entire life in a case an is in great nic).