可以看看这段英文，我出发前问服务部的人都说不清楚

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.
服务部的人说不清楚到底收不收费，在网上和客服对话告诉我不收费，我实际使用还真是这样。在一个亚洲穷国，没有Wifi，用Google Map指路，找饭馆，真是很方便。