Another big help. thanks ChrisLi. This was actually my next question after I tried researching specific smartphone models for Hong Kong. I was thinking of an Apple Iphone as that is the easiest to buy unlocked in the US before we come over and we are Apple users for computer and Ipads. Perhaps cheaper if he waits till arriving in Hong Kong to purchase, but there will many things to do in a short time frame once there, so we're thinking maybe it's worth any extra cost to have the phone in hand on landing and "hit the ground running" once in Hong Kong.

I've read that China Mobile doesn't work with all the Iphones, only certain models - looks like Iphone 6 and 6 Plus and 5s and 5c? Is China Mobile not a particularly good carrier? It looks like it is easily available for a prepaid card - at least it's the one that often pops up when I google the prepaid SIMs. Is CSL / 3 prepaid card also easy to pick up? I'm thinking he may get a prepaid card initially to use as he gets established and later get a more long term plan.

Many,many thanks to all the above posters. Our instincts and past experience would have led him to do things less than ideally.