There are two types. One is to apply to a foreign carrier outlet and provide IMEI to prove that the contract period has expired. After the application is accepted, it can be officially unlocked in about fifteen days. This type of unlocking is permanent.

The other is a hacking unlock, which is to take advantage of loopholes in Apple's activation policy and deceive Apple's server supervision through software. This type of unlocking is temporary. When the phone is restored to factory settings or the computer is flashed, it will be locked back to the original locked state.