Purchasing an iphone 15 Pro outright from Apple as an upgrade
I just have two quick questions. I'm looking to buy the 15 pro from Apple because I want an unlocked phone since I do a lot of traveling. This is my first time buying from Apple instead of upgrading from AT&T. In the checkout out I can select AT&T as my carrier or no carrier. I get a prompt that says all phone are unlocked unless purchased on an AT&T financing plan. I'm buying outright so I assume mine will remain unlocked despite choosing AT&T as my carrier. I just wanted confirmation that my assumption is correct. Secondly, I see an AT&T upgrade fee of $35 listed on the final bill (it may be put on my phone bill not sure). I couldn't really find a clean answer online. Is this something I have to pay no matter what? Say if I choose no carrier, when I connect it to AT&T later would I still have to pay that?
Thank you for your time. Also, I'm upgrading from an iphone X to an iphone 15 pro.