Towards the end of the featurephone era it became more common. And i think Nokia got into it because they had a very popular model that was found to have a nas

Towards the end of the featurephone era it became more common. And i think Nokia got into it because they had a very popular model that was found to have a nasty flaw. I still recall news reports about people queuing to get theirs flashed (this was back when GSM was the hot new system, and carriers were giving away phones if you signed up with them).