I don't know that it works any differently than the others in the handling of calls. I'm not aware that they're doing VoLTE (I suspect not because my phone beh

I don't know that it works any differently than the others in the handling of calls. I'm not aware that they're doing VoLTE (I suspect not because my phone behaves like my Verizon phone did -- dropping LTE data when I'm on a call -- on the occasion that I've had to look). It differs in handling of WiFi calling in that "it actually works really well"[1]. Calls started on WiFi switch (mostly) seamlessly to cellular when you go out of range or the call quality dives. It attaches to some public access points automatically (with a little "key" icon at the top when it does so). On the cellular front, it uses T-Mo and Sprint (and, now US Cellular). Their networks are quite different[2] and it is able to bounce between them and does so in a manner that maximizes 4G and overall coverage. There were dead zones for me on T-Mo that have perfect coverage on Project Fi. [1] I had T-Mo with WiFi calling previously and even at the time that I left it barely worked. I'd not receive calls when attached to one of my access points (or drop them if my phone jumped over to it) and call hand-off to cellular never worked for me. It always works on Fi and my phone won't even try to use the other AP for calling (which it figured out on its own). [2] I believe their 4G technology is similar enough, but below that its CDMA for Sprint and GSM for T-Mobile, I believe. My information may be out of date, though. When I signed up there weren't any MVNOs that used those two networks.