In this case, an Apple iOS update seems to have broken At&t's wifi calling. At&t wifi calling abruptly stopped working with 9.3.2 and when I contacted At&t about it, their tech suggested I switch off cellular data, switch on wifi calling and reset my iPhone 6: Every single time I want to use wifi calling. Really? Oh, yeah. And then reverse these steps when I leave the bad signal area. Every single time. I'm taking my line to Verizon. My work-issued Verizon iPhone 6 has 80 pct charge in the afternoon while my personal At&t iPhone 6 has 30 pct charge in the afternoon due to the signal strength in the building where I work. When At&t wifi calling was working, it wasn't quite this bad but now that wifi calling is broken, I feel I'm forced to move on.
My wifi calling broke last night and now today I can no longer make or receive calls. The att store said they had numerous people that had the same issue from last night.
Data works. But cellular calls fails. She said everyone that had the problem all said they recently updated their phones.
She also said DO NOT get a new sim as the customers that did switch to new sims ended up with phones that could not receive data or calls.