Verizon won't activate it, but an active Verizon SIM would work on LTE, including VoLTE.That's different.
That one you have should be fully unlocked and is CDMA capable. Can you go to settings/general/about and give me the model number listed there?
The one in question that I was referring to is an AT&T iPhone 7 and that will never work with Verizon.
https://www.macrumors.com/2016/09/08/att-and-tmobile-iphone-7-models-lack-cdma/