Tmobile now has an Apple app that allows you to order prepaid service and provision the ESIM:
https://itunes.apple.com/us/app/t-mo...437014693?mt=8
I can see from the pages shown at the link above that one of the options is the $30 "Tourist Plan."
I think this is a first - inbound travelers to the US can provision an ESIM and service before leaving their home country, and have service immediately upon arrival in the US.
I assume other carriers (in the US and elsewhere) may implement similar over time.