There have been a number of sites within the US claiming that a new HD Voice feature has been included in the iPhone 5 but not supported by their carriers.
However, according to Pocket-Lint the UK might have the upper hand on this one, as EE have confirmed to them that the new wideband audio feature works just fine.
The feature was revealed to be working on Twitter in a conversation between Stuart Jackson, and Stuart Miles from the site, in which he revealed, “Am using on EE network (obvs). Call quality crystal clear. 3G web feels faster. V.good network/phone integration.”
@stuartmiles yes indeed. The best version of it I’ve tested. It’s quite startling first time you use it – it’s so clear!
— stuart jackson (@ee_stu) September 21, 2012
If you’re not quite sure yet, HD Voice is a wideband audio technology, and will increase the frequency range allowed for audio signals, improving the audio quality.