Well, first of all, the J One is only sold in Japan and should only work on a specific carrier there - KDDI au. I don't know how you got one from China, double check to make sure it isn't a fake. Second, T-Mobile doesn't use standard international frequencies for 3G and 4G so you'd be stuck with a phone that can only work on 2G, unless you want to switch to AT&T. Third, if it's not accepting your SIM that means the phone is locked
, so unless you're willing to learn Japanese, travel to Japan, subscribe to KDDI au and call them for an unlock code, you just bought an expensive brick.
Originally Posted by L0rdNels0n
Oh Dear Oh dear
The HTC One has an INTERNAL sd card you can't insert your own
Nope, the J variant has a removable back cover with a microSD card slot.