Wow, all this information it's very useful for me, and it looks like the service it's cheaper than what I can get in Mexico, I currently pay about $90 MXN ($8.5) for 10MB of prepaid data. I'll see if I can unlock my phone later today.

My tour includes Shanghai, Beijing, Xian and Hong Kong, I'm sure that the hotels I'm going to stay have wifi, and I'm planning to make most of my calls with VoIP. The service looks cheap enough to buy a SIM card and use it as a backup service.

Thank you very much to everyone for all the useful information and comments.

EDIT: I forgot to ask if I need an adapter for my chargers, It's the same wall plugs that the US ones?