2. There are two kinds of upgrades, one is guaranteed baseband upgrade, and the other is not guaranteed baseband upgrade. After the baseband upgrade is guaranteed, the mobile phone will be used normally. If the baseband upgrade is not guaranteed, the mobile phone will continue to be locked, and only American sim cards can be used. When upgrading, the system will tell you that there is a new firmware and ask you if you want to upgrade.

3. As long as you unlock it, you can use the domestic sim card to surf the Internet.

4.SHSH is the server address authentication of the system. Every time you upgrade or restore the system computer, you should visit Apple's server to see if it is the latest firmware. If it is not the latest, it will be automatically upgraded to the latest. It's all gone after the upgrade. After SHSH backup, you can bypass the Apple server and revert to the old firmware.

There is nothing wrong with the American version, except that it is annoying to have a lock.

6. Yes, the risk is that you cut the card. .