A few years ago, I visited Tibet with friends. One of our group was a T-Mobile subscriber, and was able to leverage their roaming agreement with the PRC (and its bypassing the Great Firewall) to read and post on Facebook, among others.
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).