TMobile is kicking old Android phones off their network in January because vendors have abandoned the hardware and they no longer get security updates. Android's model of forcing you to buy new hardware every few years to get security updates is broken. https://www.tmonews.com/2020/12/t-mobile-will-no-longer-support-devices-january/
@jfred I don't know how Tmobile would know which OS is running, and I doubt they'd add that kind of nuance to their policy.
@kyle @jfred How do they know which device it is in the first place? Can you look up that information somewhere if you know the IMEI?