A:AnswerYes. When you are there all you have to do is take the sim out and place the visiting countries sim in to use, when done swap the chips back.
I went to Dubai, Pakistan and Thailand and used all those 3 countries sims with no issues.
A:AnswerYou can get a trade in amount if you trade in a qualifying smart phone, I believe qualifying iPhone . I know I was getting an $800 dollar credit with AT&T by trading in my iPhone 11pro max . But I decided to keep my phone to give to my mother