The GPS technology is the Only way of tracking ppl/things on any footprint on earth.
This is being used by government officials since it was invented.
It's only few years back it has been introduced to smart phones.
I have a Korean friend working for her embassy, she is a diplomat indeed.
She Not only switches of her phone bit also removes the battery.
So it's not just abt iPhone. It's any phone/devices having both GPS & GPRS.