In most respects, I've been really happy with T-Mobile since I switched in April. I pay much less for service through T-Mobile than I did through either AT&T or Verizon, and on the odd occasion I've had to contact their customer service (only twice so far), I've been left feeling better than I did any time I ever had to contact their competitors. However, T-Mobile shares one flaw with those other services: their coverage sucks inside my house. That's why I want Wi-Fi Calling. It's a feature that T-Mobile has on several of its Android and Windows Phone handsets, but it isn't available on the iPhone. At least not yet.