unlock iphone for temporary overseas use
Hi, I am on AT&T plan with about 22 months left on the phone payment
I have come to Korea for summer and do not want to roam because of the costs. Instead I have got a cheap local carrier plan which I plan to use for only 3 months (no strings attached). I put the activated USIM card but it seems my iPhone XR is locked and can not proceed.
1) Does AT&T offer a short-term unlocking for cases like mine? I fully intend to go back to AT&T when back in US.
2) If not, can I unlock by paying off the remaining balance of the phone payment? (Is it simply the monthly cost [$20] x remaining months  ?)
3) How can I unlock from Korea? Over the internet or on the phone?
4) Anyone know if South Korean carrier LGU+ is compatible or not with AT&T iPhone XR?
Amanda and James