Is HD voice really noticeable?

I agree with Dan, but this shouldn't get in the way of deploying VoIP. IP connectivity is growing all the time, and eventually HD will be the norm. That's a long time out, but along the way, when people hear HD for the first time, they will definitely notice. It's a bit like HD TV - it's hard to go back once you've seen it. For now, HD is really a feature, and you don't pay extra, so don't worry about it. It's a bonus at this point, and your thinking about VoIP should be focused more on cost savings and IP-enabling your communications and business processes.

There is a night and day difference between normal 3khz voice and HD voice. As the others have stated above, it is likely already part of any VoIP solution you are considering. The key is to make sure that your phones are HD voice capable. Also, keep in mind that in most cases, as soon as you call outside your company, you will revert back to standard voice. Some carriers will provide intercompany HD voice on their hosted services if both ends are subscribed to the service.

I work for a company that has pioneered many of the advances in HD voice technology, Polycom. Not all HD is created equally. The baseline is 7khz audio, but there is also 14khz, 20khz, and even 22khz HD voice. You will notice a difference at 7 and 14 is even better. Above that, it only becomes really important if you are doing any type of remote music or multimedia production. At 20 and 22khz, we have advertising firms, audio production studios, and television studios seeing benefits from 20 and 22khz audio.

All users will hear a significant difference when moving from standard 3khz voice to 7 or 14khz voice. Conversations are much more clear. With 3khz, there is lack of definition and it is sometimes difficult to hear the differences betweeen s's and f's, t's and d's. It could be the difference in choosing to "hire" or "fire" someone. It also makes a huge difference in understanding people with thick accents. Lastly, it makes long phone calls and calls in conference rooms much more endurable. You no longer have to concentrate as hard and casues less fatigue.

I don't want it to sound like any kind of sales pitch, but there is really good information on the following link from my company's website:

http://www.polycom.com/company/about_us/technology/ultimatehd/hdvoice.html

There are whitepapers on the technologies and advantages of HD voice. Also, there are links to real audio clips of HD and non HD voice.

As Jon said above, once you go to HD voice, you will never go back.