The TMobile website seems to have a lot of conflicting information on this. I *think* the current answer is that TMobile prepaid services can only be used in the US, Canada, and Mexico. I wouldn't be surprised if your wifi features (wifi calling, text, data) worked elsewhere, but that would be a roll of the dice. If you were going to travel i'd look into a local prepaid sim at your destination or just going with TMobile post-paid.
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