Because VOLTE is voice over LTE and that's simple to figure out the answer is yes.
https://en.wikipedia.org/wiki/Voice_over_LTE for a primer on this.
That doesn't mean your average phone can't make voice calls, but no phone yet is only 4G LTE/VOLTE.
I guess when there is network problems, phone automatically falls back to 3G/2G. But if phone is only 4G LTE/ VOLTE, then does it stop working if 4G network is down?

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