I went to a China Mobile customer service center today and signed up. The good news is that it's very possible to do this; they don't care what kind of visa you have, tourist is fine. The bad news is it took 2.5 hours and five employees. No one could really figure out the process so they kept sending in someone new.

I got offered postpaid (Y200 for one time setup fee as bill credit, 1 year contract, Y40 for 12GB*). I guess there was a prepaid contract but 40 sounded fine and the guy was pushing it. It is for 5G, but my phone is too old anyway so it doesn't really matter.

You have to do a bunch of stuff like get fingerprinted, picture taken, and record a video saying "I got this number and I will follow the laws"

* 5GB province-only data + 5GB anywhere data + 2GB data that will start next month