We’re probably an exception here, if only because our smartphones are 5.5 years old (and were 3+ years removed from initial release when we purchased them as new old-stock). We’re looking to drop AT&T, mainly due to text messages being lost (sent and received), so new phones and a new service it is.
Don’t get T-Mobile. We switched from Verizon a couple years ago and the T-Mobile service is HORRIBLE. Unreliable, voice quality so bad you cannot understand anything, dropped calls, no ringing on incoming calls, ringing on incoming calls but call won’t connect. What an incredible waste of money.