How many people out there are actually willing to change carriers??
Take my advice - A SGS2 user, bought an unlocked iPhone 5 after T-mobile announced Minneapolis is refarmed. Lousy coverage. I have Edge most of the time, and when you do see 3G on your iPhone and you enter a building it switches back to Edge. I frequently have seen no service on my iPhone 5, which I never see on the T-mobile HSPA+ network. I switched back to SGS2. The refarmed 1900 Mhz 3G compatible with iPhones is worse than Sprint. You get what you pay for. And there is more..! T-mobile while claiming 120 million US population covered in 40 cities, it refuses to put 3G coverage maps!
Coverage varies for everyone.. I'm in Orlando, this is with an iPhone 5. Check airportal.de for coverage. Also, there is performance differences between HSPA+ on 1900 and on AWS, at least here in Orlando I have friends on AWS HSPA+ that get consistent 20MB+ performance on their phones.
HSPA+ on AWS does not work for iPhones. So that discussion is irrelevant here. The fact remains that T-Mobiles 3G running on 1900 MHz is spotty and Eakins. The higher frequency is unable to penetrate buildings and will be poor laggard among the 4 national networks. No iPhone has got 20 Mbs + on T-Mobile network. I challenge you to post those speed screen capture shots.