Both ends need to support wideband codecs, as does your phone (hard or soft phone). This includes the VOIP providers needing to be able to use wideband codecs between each other.

If you achieve a wideband setup the call quality is amazing. I've used it for years. It really sucks when you have to call someone on a legacy POTS line or using a narrow band codec (bad voip, cell phones, etc)

On that note it's unfortunate that cell phones which can do wideband codecs within the same carrier (HD Voice!) won't work if your call leaves their network.