Calls will be charged and texting is free.

https://www.t-mobile.com/coverage/international-calling

I think @gramps28 was confused. St Thomas, USVI has three native T-Mobile LTE towers. Additionally, you may find yourself roaming on Innovative. This is handled as domestic roaming. If you have an Android phone you might want to install CellMapper and run it during your visit.

I think it was the British Virgin Islands that popped up instead of the USA Virgin Islands.

there may have been changes in a years time so let me ask is St Thomas part of simply global?

I think it’s still domestic coverage.

Will my T-mobile phone do phone calls, text, and internet while in St. Thomas US VI.  If so,  are there any charges?  My phone is a I-phone.  will Maps work.  

Yes, T-Mobile has 100% 5G network coverage in St. Thomas and the US Virgin Islands (USVI). T-Mobile also has retail locations in St. Thomas at Lockhart Gardens Shopping Center and in St. Croix at Peters Rest Shopping Center. 

https://viconsortium.com/vi-technology/virgin-islands-t-mobile-officially-arrives-in-usvi-boasts-100-percent-5g-network-coverage