My wife and I have been using Skype for about a year. It's been very handy. We bought a US number so the whole wham-damn family can call us cheap, and also leave voice mail. Calling land or mobile phones is cheap with Skype credit, so waiting for the receiving party to get to a computer is barely worth it.
I don't know about all HK serviced apartments, but I was in the Horizon in Ma On Shan, the internet service there was pretty good quality.