Also, there's currently no LTE roaming agreements
At least there aren't any that I'm aware of. IOW, if you require the fastest data speeds on your device, you would only get them while using a Verizon branded iPhone while still on their U.S. network. It would throttle down to what the foreign carrier offered. For most this is not any sort of deal breaker, just good to know if you have expectations about how a device will perform outside your home area.