Originally Posted by
LordHamster
FYI, in China T-Mo iPhones will have issues with LTE access. Due to T-Mo's roaming agreements, they roam in China on LTE bands not supported by T-Mo's iPhones. You will be better off buying an unlocked (sim Free) iPhone Model from the Apple Store, or their Verizon version. THEN pop in the T-Mo sim.
Seems to depend on which iPhone you have?
On iPhone 7, the set of supported LTE bands is identical between the two USA models.
On iPhone 6s, the set of supported LTE bands is also identical among the models, EXCEPT that the AT&T model supports one extra band that's seemingly not relevant in China (band 30, 2300MHz).
iPhone SE, iPhone 6, and earlier might have some relevant differences though.
https://www.apple.com/iphone/LTE/