I looked at CNN's chart to see who has LTE built out where. Verizon has LTE everywhere, At&t has it in about 15 cities with the closest location a 4 hour drive from here and Sprint has it in only about 5 cities. I looked at my At&t bill and it shows my rate plan changing in December from 2GB 3G data to 2GB LTE data in December. My iP5 is supposed to arrive well before then so I can assume At&t intends their 4G LTE in my area to be built out enough to at least bill for it by December. Bottom line: I'll be leaving mine switched off until I'm sure it is built out enough to actually use. At&t's 3G is so much faster than Verizon's 3G, I'm sure it will hold me over until there's enough LTE buildout in the Detroit area to justify leaving it on 24x7.
This is one of the areas Apple really needs to rethink. On an Android device, I could get a 3rd party "profile manager" to switch on LTE at specific times of day. On iOS, that's considered something apps shouldn't be able to touch.