可以看看這段英文，我出發前問服務部的人都說不清楚

Only T-Mobile’s network can give you unlimited everything for everyone. Other carriers may even make you share minutes, messages, and data between you and your family. With our Simple Choice Plan, each line comes with unlimited talk, text, and data while on our home network. And now, all your lines can enjoy an additional 500MB of 4G LTE data and tethering, plus unlimited data and texting from the US and abroad in 120+ countries and destinations. That means no overages just about anywhere you go. Plus, there's no annual service contract and it's easy to add additional lines.
服務部的人說不清楚到底收不收費，在網上和客服對話告訴我不收費，我實際使用還真是這樣。在一個亞洲窮國，沒有Wifi，用Google Map指路，找飯館，真是很方便。