Haha. You are wrong.. I have had T-mobile for 7 years, and have not had an iphone up until the past month. Their coverage on their frequencies was great when I had my android.
Now that I have the iphone 5, I have noticed a significant increase in the 3G areas and it is getting better and better. Yes, its still a little spotty, and not very good in buildings yet, but they are continuing to update the service. When my phone says 3G, it is super fast - I don't even desire LTE because of this thing called wifi.
Also, I use wifi when I am at home, or whenever there is wifi around for me to use... and plus T-mobile plans are CHEAP and the service is not that bad.
Finally, since they are getting the iphone 5, they are obviously confident in getting their new service to the areas that they currently cover, and the millions of people with iPhones that are trapped by Verizon and AT&T might finally wake up and flock over, because quite honestly they're getting ripped off