Wow, we still haven't got wide spread availability of 'HD Voice' and we're fast approaching 2012.... Then again the UK looks set to be one of the last European countries to jump on the 4G bandwagon as well.
I hadn't looked at this for a bit but just did a quick check and its good to see that Three jumped on board this year to join Orange with availability but it would seem other operators are still dragging their feet.
Probably the upgrade is costly or they are concerned about the disparity when their customers fall outside a 3G coverage area (required on both HD Voice handsets in order to function).
The magic phases you want to look out for our:
Anyway, for more info, check out the Wikipedia link: