Verizon says that USVI is part of the US plan and therefor no roaming charge.
However in 2017 I did get roaming charges while in Charlotte Amalia.
Verizon said I might have picked up a BVI tower, but I am pretty sure that was not the case.
They refunded all charges incurred during my time in the USVI.

Heading back down in a 2 weeks. We will see if anything has changed.