There is indeed GSM in parts of China, but only 900 Mhz.
You will need a -30 or -90 suffixed model BlackBerry to roam voice/SMS on China Unicom 900 Mhz GSM, and China Mobile 900 Mhz GSM.
At the moment, no GPRS roaming is supported. Just voice and SMS. No email.
For China Mobile 900 Mhz GSM coverage (Rogers Roaming): http://www.coversoft.com/cgi/imap_ro...=cn&net=ct
If you have a 7230 BlackBerry, it should support roaming on China Unicom or China Mobile if TMobile has an agreement with them. But it may be voice-only roaming.