As a Verizon customer, the release of iOS 9.3 brings my first hands-on experience with wifi calling. I noticed at home on wifi it says "VZW WIFI" as the carrier name in the top left corner as expected. Today, I'm at a Barnes & Noble bookstore on their free AT&T wifi. Though I have a working wifi signal (as evidenced by this post), the carrier name has not changed, so I'm presuming something is stopping the phone from switching to wifi for voice. So, if anyone knows, what are the conditions that tell iOS that it can switch to wifi for voice versus LTE (or, god forbid, crappy Verizon 3G)??