3G services in China:
China Mobile = TD-SCDMA
China Unicom = WCDMA
China Telecom = CDMA (EDVO compatible)
China Mobile's 3G network has been horribly designed and poorly managed making it incompatible with ipad2, and works only on GSM and only compatible with AT&T version of ipad2
Currently China Unicom's service works for both roaming and for local subscriptions with the AT&T version of the ipad2. That said Unicom's 3G service is very spotty and often unreliable, but is really the only mass market option for local sim cards / use.
China Telecom CDMA works with Verizon versions when roaming in China. Best 3G service, pound for pound, is China Telecom, but right now 3G ipads are not being sold in China, which means China Telecom is not offering local plans (yet). Because the Verizon version of ipad2 dont carry a sim slot, you cannot get on to the network with roaming (which is expensive) until China Telecom supports and publishes the hack.
Although engineers in Guangdong branch of China Telecom hacked the Verizon iphone4 to get it onto their network, but so far no one has published a solution for the Verizon ipad2.