I hope TMob does it too but it may be tougher since they have way more customers than Google Fi since that service is limited to a couple of Nexus phones.

The thing is, a lot of these roaming partners actively market and target travelers for short term data use so you wouldn't think they'd just give roaming data to TMob customers for nothing.

Then again, EU is suppose to have free roaming by the middle of next year so maybe the economics of mobile data are changing.