Verizon also will mark your line as hotlined, disabling all functionality if you use a device that works but they don't like or if your late in payment or trip up another undisclosed trigger.
I wonder how long I have on T-Mobile, I keep getting texts like "T-Mobile: Action needed. VoLTE settings may be affecting service quality for phones on your account.". On this particular account there is a single Nord N200 5G bought from T-Mobile, and as far as I can tell VoLTE works fine on it.