Some people and companies have a hard requirement to set TFA (Two Factor Authentication) to secure their dashboard login from password leakage.
And normally, using SMS (service provided by Telecom Carrier, e.g. China mobile, China Telecom) is a very common method to do so.
But our experience and many issues were reported from such end-users show that You can indeed enable SMS TFA, but you basically will never have it working when login to your dashboard.
We will strongly suggest that DO NOT enable SMS TFA with China mainland mobile numbers (it seems if you are roaming to China with a US number, it would still fail).
Please read the dashboard banner carefully before you enable it. It clearly stated that SMS TFA is only validated in the US and UK.
In order to secure your dashboard login as per your company requires, please enable TFA with google authenticator app, this is an offline tool, you do not need to connect to internet/google service when using it.
So please do not worry about the unavailability of Google service in China.
Another option is to use the "one-time codes", Meraki dashboard will list you with 8 codes, so please copy and paste them into a safe place for your future use.