I forgot to add a couple of things:

1. The WiFi calling is great, but if you find yourself in an environment where there are restrictions on the availability of the WiFi to a personal device (such as in my office) it may not be a huge help when the providers own signal cannot penetrate the building well. Nothing frosts me more than people that just blindly assume that "free" WiFi (without restrictions) is as ubiquitous as water.

2. Starting 9/17, T-Mo will be offering Personal Cellspot devices (think Home WiFi Router) that will augment WiFi calling performance substantially.