Yes, it works, but the codec itself is very bad. Not to mention if the server is lagging so will the voice function. It's just not a reliable way of speaking to people in raids. There _MIGHT_ be people using it in the US as it is far more likely everyone will understand, but probably only on random dungeon.
Speaking of which, why is this in Interface & Macros?
No. We use Ventrilo. In game voice chat is a good idea but at the same time a terrible one. If someone d/c's or has horrible lag or anything of that nature, it's nice to have a way to communicate that with the group, raid, guild, etc.
I only tested it the date of release and I found it hellish to use so I never tried it again. They may have improved it, they might not have, who knows. All I know was that I had to turn the volume up all the way and still could barely hear people and the quality was poo.