It seems like Samsung has made some changes to the international Exynos Galaxy S9/S9+ and not all T-Mobile 4G LTE bands are supported this year unlike previous Galaxy phones. AT&T is not affected but if you are on T-Mobile, just know you may get stuck on HSPA+ most of the time if you buy the international Exynos Galaxy S9/S9+ models.
SM-G960F, SM-G960FD, SM-G960F/DS
SM-G965F, SM-G965FD, SM-G965F/DS
A good alternative is any previous Galaxy international models like the Galaxy Note 8, S8, S8 Plus, S7, and S7 Edge, they all support T-Mobile 4G bands fine.
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