Cause both areas are side by side, would the same simcard work in both locations? I am only going to shenzhen for 2 days and staying in hk for the remainder of my stay.
You would have to use roaming. There used to be sims that would work in both places, maybe still are, but they were much more expensive.
Either you have to get a SIM that supports roaming, or you have to get two-country SIM.