AFAIK, t-mobile phones will not work on verizon's network.
I'm in the same boat as you, debating on switching to t-mobile, but I'm nervous about Data speeds and coverage
If you have lte, data speeds are great. Look at their coverage map, it is pretty accurate. Also, look at opensignal.com
If you share with us the area you live/work...someone here might be able to help you more.
Ya, I was just lazy and waited till the 6 was about to come out and of course...I...WANT....ITNOW.