I haven't had this problem with AT&T international roaming in China (which essentially bypasses the firewall since it tunnels back to AT&T's APN) but then again I haven't been to China in 2 years.

My guess is that their Huawei WCDMA network is oversold. Now it certainly isn't a equipment problem since the same Huawei equipment is used in Canada and Europe without any problems (they innovated with IP RAN). I guess they really need to increase cell site density. I believe Unicom's network in the major cities in China is already the latest 21Mbps which also increases spectral efficiency.