I'd like to get my wife an iPhone 6 (at full retail price) now but we have a bit of a catch. We're moving from the US to Australia in a few months. We're currently on Verizon. I'd like for her to be able to use it for the next 2 months and then swap sims when she gets to Oz. When we travel back to the US, we'd like to use it on TMobile prepaid. So will a Verizon iPhone allow me to use it overseas or on tmobile? Or should I buy AT&T or T-Mobile iphone and can that be used temporarily on Verizon?