HD Voice is on a growth path. Some say slower than expected, some say faster than expected. Like many things, that is dependent on your point of view. One way to measure growth is the amount written about a topic. There is an HD Voice News site that I visit from time to time. And a quick search yields quite a few articles - here is a recent one talking about mobile VoIP and here is one in Polish - I don't know what it says (though it seems to be talking about telepresence) but it clearly says "HD Voice" in there, as well as "HD Video".
Another way to measure growth is my use of a new technology. I'm about to get an HD capable phone at work, so I'll be HD enabled soon. Basically I'll be voice enabling my email address. There is a whitepaper at siptosip.net that explains how this works. I won't be able to get to the PSTN, but I'm looking forward to making some HD Voice calls and I'll let you know how it goes.