A:AnswerWe went from S4 to S10e. We did need a new Sim (newer tech?) and it was provided free of charge by Best Buy. They transferred all of our data and got us up on our existing Verizon plan. My guess is AT&T would work the same. In store tech was great.
A:AnswerIt doesn't matter. Once you insert your sim card, the phone will configure to that network. There may be additional settings needed to access a particular network's data service.
I don't believe they ask you if you want to activate today or later. The phone is unlocked.