According to this article it seems that the Sprint-Tmobile merger is still on... https://www.foxbusiness.com/financials/t-mobile-sprint-merger-nearing-completion-after-controversial-and-lengthy-negotiations.amp Sent from my SM-G975U1 using Tapatalk
You won't be charged roaming while in the USA. Period. End of story.
Turn on data and enjoy. Talk and enjoy. Text and enjoy.
VZW/ATT data will be slow/unusabled and you only have a 100MB bucket. After this bucket is used you are cut off. Everyone else data experience should be usable and treated as if native.