I will be going to the Philippines soon

Hey there! If you have a postpaid Simple Choice plan, roaming in the Philippines should be pretty awesome! You can take a look here -- Planes internacionales | Viaja al extranjero sin cargos por roaming | | T-Mobile for details. 😊 I'd definitely recommend scrolling down and entering your device type to check compatibility, and then if you know where you'll be staying you can also input your province or city in the box above and to the right of the map to see more detailed coverage.
Lastly, we have an Lista de control de roaming internacional that can be super helpful to review (and save) before you go, because it includes our roaming care number in case you need to reach out while you're abroad.
Please let us know if you have any additional questions -- hope you have an awesome trip!