Cellphones in China.....

I need some advice. I am new here and I need a question answered. I will be traveling to China this year and wish to have a cell there. They use GSM networks in China, so I was thinking of buying a Nokia 6600.
There are two types of SIMS you can get for china. One is a prepaid, the other is a monthly service type of SIM chip.
My question is if I unlock the phone will this give me access to all availible services? Or does the SIM chip make the services availible.
Basically the prepaid you get voice and SMS. The monthly you get internet and every other service.
Personally I would rather have the prepaid if I could get all the other services with it.
Thanx in advance! :-)