I thought this was the case too but after falling victim to these tactics myself, AT&T began to actively hold my numbers hostage. In my experience AT&T requires

I thought this was the case too but after falling victim to these tactics myself, AT&T began to actively hold my numbers hostage. In my experience AT&T requires you set up a "TRANSFER PIN" that you give to the other carrier when porting, but in my case have repeatedly rejected the request with the correct PIN. AT&T is a incredibly consumer-hostile company that does not play by the rules, can and will hold your phone numbers hostage, and as shown here will arbitrarily disable devices when it is convenient for them.