This has worked for me. Settings > General > About > Network Provider now updated says "Three 64.2". Rebooted the phone and now Wi-Fi calling is back up and running. Thanks @WelshPaul without your help I'd still be in limbo!
I noticed this on Sunday 8th June. Good to see Three and Apple are working to resolve it.Are you saying it only affects iPhone, and is working okay on Android??I'll give you until the end of the week if it's not fixed by then, I'll ditch Smarty/ Thre...