I will travel to China via Hong Kong airport (stopover only). I will stay there for 4 months. I heard that it could be useful to purchase a SIM card at the HK airport because you can use it in the mainland as well and what's more, you would avoid the necessity for VPN on your mobile.
Can you confirm this? Or would it be better to buy a SIM card at my final destination in the mainland? If not, could you also suggest a concrete SIM card from a certain provider?