3g data sim in HK/China

[squicky]

I'm heading over to China for 2 weeks then HK for 2.5 weeks before returning to China for another .5 week soon.

Anybody have any ideas on the cheapest way of sorting out 3g access on my phone whilst I'm over there?

I'm wondering if trying to get a HK PAYG sim and roaming in China would be more convenient (assuming that the data roaming costs wouldn't be too high...) or whether I need to get a PAYG sim from the likes of China Mobile and then whilst I'm in HK get a similar sim from 3.