Factory unlocked phones have no issues that support all the carrier,But if the problem with Gevey users that is panic after the update of last or who wish to change the new carrier.After the update of the 10.3.3 most of the gevey users
have problem with activation error.I found the solution and wish to share with the friends who got that problem.The solution is you need to jailbreak the phones,Remember that makes your warranty void.
You have to remember that activation server only works on IOS 12.3.1 till date.The iccid that you can`t put on that ios because apple disable the emergency call input ICCID function too.This [https://youtu.be/HN4pE8kk43Q|tutorial] is helpful for those friend who encounter with that problems.