I switched to TMobile earlier this month and got some "no service" areas in my house. I thought that the signal booster would be the answer BUT the guy in the store assured me that if I turned on "WiFi Calling" in my settings, that would help immeasurably. It has. Now I am calling on my wi-fi set up.
TMobile is very much less expensive, and my expensive AT&T service dropped calls pretty frequently. I did have my iPhone 5 checked at the Apple Store and it was not the fault of the phone but of the carrier.
So far, so good. Love the unlimited texting (had no texting on my AT&T plan), unlimited talk, and data (had something like 2 gigs on AT&T and they made it sound like I had 400 Gigs). I am in Cincinnati and so far, no complaints. I don't think that rural coverage is going to be very good at all, but AT&T was really spotty out there in rural land, too.