Should i unlock an iphone 4 to work on t-mobile?

I was wondering if i should go out and buy a nearly new iphone 4 set to work on at&t, but have it unlocked to work on my current carrier t-mobile. I know that tmobile is switching to its new LTE network but i don't know if i live in an area that is already supported by it or not. I live in austin tx. If i do live in an area that is supported will it have all the same features and be able to do all the things it would on at&t or would i be sacrificing somethings for the switch?

Apple won't release an iPhone 4 to be compatible on the LTE network. The 5 will work on tmobile a LTE in a coverage area on they launch it, however, the 4 is not designed for it.