One thing I’ve been unable to answer is whether the monthly credits would be jeopardized in the following scenario.
Keep the iPhone 12 in a drawer as the payments+credits are still being applied monthly, and buy an iPhone 13 or 14 or whatever completely outright (full price, unlocked) and use my SIM card in that. I’ve heard conflicting thoughts on this.
As an aside, I hear people saying 'swap sim cards', and I've never had that work. I have always had to go crawling back to the local AT&T store and get a new sim, and have that sim applied to my account. It's never worked right, ever. THat's why I have a dim view of the whole thing. *shrug*