Some Hong Kong sims can roam in China outside of the great firewall. Also, it used to be kindle would work in China on twice of the GFW to, for some odd reason.
Right. Conversely, if you are a foreigner in China with a non Chinese Apple account, you skip the Chinese server as well. This is just a matter of setting your country, and you can still use the Chinese App Store if you wish (just set it to China, install app, then set it back to the USA).
Also, if your iCloud country is set to China it doens't matter which country you're in or what SIM you use; your iCloud account will be stored in a Chinese data centre: https://arstechnica.com/gadgets/2018/01/apple-sends-icloud-c...