I'd imagine much like EE's equipment upgrades ie 2G refresh that call quality has likely improved along side better backhaul.. but is it HD Voice, unlikely.
Originally Posted by japaul:
“I've not seen (or rather heard it) but it is coming as they said Spring would provide HD voice "everywhere" in their controlled European footprint. As it's Spring though that could mean anytime by March 2016.”
If they were to turn it on, would that mean O2 also? They would benefit from it the most..