Regarding use of new iPhone x

When and where did you buy the phone? Apple didn't sell unlocked iPhone Xs in US until December 4.

http://appleinsider.com/articles/17/12/04/apple-starts-sales-of-sim-free-iphone- x-models-in-us

Some stores, such as Best Buy, sell, iPhones that they claim are unlocked, but those phones require US SIMs, and will lock to the first carrier used.

While the iPhoneX and 8 have been sold unlocked since day 1, until recently you would have needed a number or account with one of the US carriers in order to buy one as clients from the carriers were given priority.

However, you would have had to purchase it from the Apple Store as Apple is the only source of unlocked phones.

BestBuy does not sell unlocked phones. You phone is locked to a carrier and only the carrier can unlock it.

Moral of the story: buy a phone in the country you intend to use it in.