I have the Galaxy S8 Korean model (SM-G950N). Data service will work, but voice and SMS will not work. The specific model is not compatible with the Verizon Network.
I have already tried tinkering with the bands/channel/network type settings on the phone, but I have no luck getting voice to work.
I had a job overseas and my old Galaxy S6 was "dying", so I bought a Galaxy S8 through Olleh KT when I was in Korea. Before I left, they said the phone would work with U.S. carriers. Apparently, not completely with Verizon Wireless, as I had found out.
I work in Germany now, where voice, SMS, and data works fine with the Galaxy S8 from Korea. Vodafone is my current phone carrier service.