I just switched to T-Mobile with my iPhone 5S, largely on principle. My monthly bill won't go down much and my service has gotten worse, but I'm so happy to leave AT&T and support what T-Mobile is doing. The new international roaming policy is icing on the cake.
Really? I did the same, my bill went down 50% (this is on top of a sweet discount I had on AT&T). But I see your point, I'd switch even if the savings weren't as good, they treat you like real customers, not sheep.
5GB of 4g internet with 3g speeds after that, unlimited texting, and 100 minutes of non-wifi talk (unlimited on wifi) per month is only $30 flat on T-Mobile if you buy the start-up kit at Walmart.
If you need more minutes than that you can either call over wifi, pay $0.10/minute or talk all you want for free over Wifi/3g/4g using a VoIP app like GrooveIP.