Earlier quoted context omitted.
Before the iPhone, how prevalent were software updates to phones? I know of no one who ever got had an update. There is absolutely no reason for carriers to need to do anything at all, else it would not make sense that I can change the SIM card out and voila I’m on a new carrier. The manufacturer is the one doing the testing, and the carrier simply provides the infrastructure. I feel US perhaps has a different experi…
It's not just just Verizon. AT&T, in particular, has a habit of locking important features (VoLTE, Wi-Fi Calling) to phones running AT&T-branded and certified software. So unless the device you want is sold by AT&T and you get the AT&T-branded version, you're SoL. They even do IMEI blocking, so even if your device could otherwise work...
In particular when Nokia tried to introduce SIP support.