Hi all, looking for some advice on what kind of SIM products are there that allows one to get 3G on iPhone with data roaming.

So in the past, I have tried these 2 solutions from China Unicom
- monthly plan, for 60rmb/month you get 300mb data, allows data roaming to any other cities within mainland china. Problem with this is that you need to register with your passport (not a huge deal, takes ~30min). But you must continue to pay every month, and you must go into store for cancellation - this isn't as economical as I go there maybe once or twice a year and staying for a few weeks each time
- prepaid card, i think something under 100rmb for voice and 300mb of data. Problem with this is that data roaming is not included. eg. if I buy a SIM card in beijing and go to shanghai, my balance will drain in a few minutes because the included 300mb data is only for within beijing. I could buy another SIM card while in shanghai, but that meant a change in number and other people will not be able to reach me anymore.

So I'm looking for the following:
prepaid/pay as you go (so that for the majority of the year when I'm not in china, I don't have to pay)
SIM card/phone with data roaming (to avoid outrages roaming charges when moving between cities in china)
3G on iphone (I'm guessing China mobile is out of the question)

Thanks in advance for any suggestions!