You won't get 3G in China because this hasn't been adopted there yet, and WLAN is not allowed due to government regulations. Instead, the Chinese use WAPI. If I were you I'd consider to buy a cheap Chinese device in China instead leaving your normal devices at home.

If you have an unlocked phone you should be able to phone with it using a prepaid SIM card from Chinese telco. GSM _is_ supported in China, and I think GPRS as well, but don't pin me on that.

Also, don't expect people in China to speak English. Be surprised when they do. Although I believe in Hong Kong downtown you'll have more chance than rural areas.