1. If it is a lock-free machine, that is, a non-contract machine, at present, the T-MOBILE contract-free version of Apple official website in the United States is lock-free according to Apple's statement, but it is not used for all domestic networks, and only supports GSM\WCDMA\FDD LTE, that is to say, it only supports China Unicom's 2G\3G\4G and mobile 2G, but does not support mobile 3G\4G, and telecommunications is still ruthlessly ignored.

2. The operator's contract machine has a locked version, so it can't be used directly in China, so it needs to use a card sticker. Generally, the locked machine is much cheaper than the unlocked machine in China, but it is inconvenient to use and the system can't be upgraded at will.