Thanks for the responses!
E) T-mobile is great at home (in the city) but it is hit or miss, not close to the coverage in many suburbs. You could easily do a $30 prepaid to test it out with your current phone.
Nice idea, but, I have a 2-year old iPhone 5, Apple updated the HSPA+ frequencies in the iPhone 5 hardware 1 1/2 years ago (Apr '13) to be compatible with T-Mobile, then officially made iPhone 5 available for T-Mobile, (so iPhone 5 wouldn't get EDGE in those areas instead.), so mine won't give me the whole picture.
Try their Test Drive program and see if in a week T-Mobile works for you. Sure you'll only get a 5s, but it'll give you an idea of how the network works in your area.
I'll be moving (by January) also, and I travel, so, just trying to get a general idea of people's experience w/T-Mobile.
TMO also supports Wifi Calling on iOS8. So if you're home or somewhere with wifi but low cell signal your phone will still be fully functional.
Yes, this and the wifi box they are including helps with the fact they aren't up there with AT&T & verizon on coverage yet.
I was listening to a podcast about iPhone 6 and they talked about carriers too, one on T-Mobile mentioned that iPhone 6 isn't compatible with some of T-Mobile's new frequencies...From wikipedia: "On February 25, 2014, T-Mobile announced in their Q4 2013 earnings call that their 4G LTE network covers 209 million people in 273 metro areas.
They also plan to start rolling out their 700 MHz A-Block spectrum by the end of 2014, which by the end of the roll out will cover 158 million people. This spectrum will lead to improved LTE coverage overall in these areas, particularly indoors.[66]"
This is really the only negative: The 700 MHz A-Block spectrum of LTE is channel 12...this channel is absent from the list of channels iPhone 6 is compatible with

this is disappointing, this frequency is supposed to penetrate buildings better than their other frequencies, but, mainly, I'll be missing out on LTE in these areas.

I'm surprised Apple isn't keeping up with this, they upgraded iPhone 5 with a minor update in April '13 to add T-Mobile HSPA+ frequency, so that iPhone 5 could get this instead of EDGE where LTE wasn't yet available, and that's when Apple made iPhone officially available to T-Mobile.
http://www.apple.com/iphone/LTE/ (700 b & c listed (ch 13, 14), but not 700 a (ch 12)).
(more from wikipedia): "On March 13, 2014, T-Mobile announced a new plan to upgrade its entire 2G/EDGE network to 4G LTE. They expect 50% to be done by the end of 2014, and it to be "substantially complete" by the middle of 2015.[67]"
On the other hand, they are updating and expanding coverage quickly, and no one has said to me that T-Mobile sucks. Wifi calling, wifi hotspots, and the wifi handoff box all help also...plus the fact that the LTE they do have is faster than AT&T (sometimes AT&T's LTE feels slower than 3/4G). So, I think coverage will only get better. Since AT&T's merger acquisition didn't go through, T-Mobile has really been improving. (I'm glad, if that had gone through, Verizon would have bought Sprint also, and, (either way) I think cell service prices would have gone up for everyone.)
I'm leaning more toward switching. Now I prefer to buy an unlocked iPhone 6, and keep my iPhone 5 as iPod touch & spare camera, so, sometime this October -December.
Anyone else want to chime in?