iphone upgrade citizens one loan

I’m used to using Apple iPhone upgrade program and I usually get the promax version like 15 Pm in current have, I left AT&T in June to come to a carrier called US Mobile because the cell service is cheaper and it uses Verizon towers. I’m guessing I’m going to have to fork out the $1800 upfront for the 16 promax because I’m no longer tied to main carrier which was AT&T… is there a way to bypass this because I would assume that if I go through the iPhone upgrade program when I receive the phone, I won’t be able to activate it because it’s not tied to a main carrier… the new iPhone 16 Pro Max will be obviously coming out next month so what should I do? I have a iPhone 15 pro max on the Apple iPhone upgrade program citizens one loan