AT&T sim switch question

[AdamInTx]

So my daughter currently has an old iphone 5 that she strongly dislikes. It was an old AT&T device that we just connected to a new line on our account. I've recently acquired a used AT&T Galaxy S7 and was wondering if I can just swap out the sim card and be good to go or if I need to bring it in to AT&T and be forced to pay an activation fee before it will work.

Also, a second question. This S7 is on Android 7.0.0 with a May 2017 security patch, however, when I check for updates it tells me it is up to date. I know this isn't true. Is it possible to force it to update to the newest updates? Is this because it doesn't have an AT&T sim currently in it? Will it update once it knows it is an AT&T customers phone?

 

[Rukbat]

I haven't paid an activation fee to AT&T since about 2004. That's why GSM SIM cards - just swap the card into the phone you want to use. (It will sometimes cause the account to reprovision, then when you swap back you'll have to bring the phoine into their store (company store, not affiliate) and drive them nuts trying to figure it out.)