The two carriers that are visible to most mobile phones here are China Unicom and China Mobile. China Unicom uses the HSPA family of technologies, while China Mobile is using TD-SCDMA. If you are bringing “3G” handsets from outside China (such as an iPhone or ROA Android phones, or Blackberries, etc), you will NOT get a “3G” data service on China Mobile, but will be relegated to the slower “Edge” data service.
If you want “3G” service, you will have to manually select Unicom.
Remember, data roaming may provide you with a nasty present in the form of a bill on your return home.