I frequent HK about 4 times a year, I go to a China Mobile shop and buy an IDD card for 85-100 HK$, for that I can call pretty much anywhere in the world at very cheap prices.
They offer a data plan as well, so maybe another 100 HK$ for a week, you can chose short service - 1 day or longer 3-5 days I think, I usually pick a 5 day setting.
On top of that the sim will work in almost every country in the world and roam, but that is NOT cheap.
If I pop over to mainland China from HK then for .65 HK$ per day I can get a CHINA mainland number for the same sim and have pretty reasonable roaming rates until I return to HK.
There are plenty of options available in HK for a traveller and the phone etc, this one seems to play on the ignorance of the traveller - why would I want to have to learn another device / transfer data to it when I have a perfectly good one already.
I also recall there was an Orange service in HK that was pretty good, but I couldn't find it a couple of years ago so I switched to China Mobile /PWCC.
BTW, Google maps on Andriod allows you to cache where you want to go before you get there, all you have to do is set the option on and then prowl around HK on the map and then it is available offline on your device without needing an expensive data plan.
Happy travels folks,