[kalleboo]

If you are roaming and using the T-Mobile APN, then you're still going through the T-Mobile data infrastructure.

When you're in China and roaming on a foreign operator, you're not affected by the Great Firewall since you're data goes through the APN in your home country.

[privong]

Okay, thanks for the clarification. I did just check and I have an American geolocated IP, consistent with what you said.