Re: Forward thinking?
Many carriers want to reallocate their 3G bands for 5G services. Since 5G NR is supposed to use a new air interface and is not part of the LTE family, carriers will have to roll it out parallel to their existing LTE infrastructure.
The problem that I see is that most early LTE phones lack native VoLTE support. They use 2G/3G for voice. So when those older networks all go dark, not only will all of the 3G-only phones go silent, but so will a good number of 4G phones unless the carrier includes a VoIP app that can work over LTE data.
Here in the States where "branded" carrier-specific models are the norm, this will be made more difficult in that carriers generally refuse to support VoIP/WiFi-Calling on anything other than their own phones. They've baked their custom VoIP dialers into the firmware. So if you purchased a carrier agnostic model or brought your unlocked phone over from another carrier, you'll have to ditch the phone or find a third party VoIP service that works with downloadable app.