Read enough on this board to want to try my luck getting a "device-only", unlocked iPhone 5 from store. The question is...which should I get? Verizon or AT&T? I plan to use this with either Straight Talk or T-Mobile. I understand the Verizon comes unlocked, but is it compatible with GSM 3G/LTE? What about the AT&T version? If somehow I want to switch to Verizon, will it work too? Basically, my question is...what's the difference between AT&T and Verizon iPhone 5? Give me the big picture and don't skip the detail.