Btw, MTR in HK just started a free wifi service in all of their stations. The problem is that the covered area within the station is pretty small. There might be only one hotspot in the entire station. Hopefully they will expand the coverage in the future.
Might be a hit or miss at certain locations / area you were at.
You should be able to get reception almost always at the platform. I could even connect when I'm still in the train / just waiting for passengers to unload/load.