How does my iPhone change time zones automatically? I'm curious how my iPhone knows what time zone I am in and change automatically. Does the phone use GPS to figure out where I am in the world? Or is there some other technology in play here.
It uses a combination of GPS and the date/time sent to the iPhone from the cell towers.  

There's several questions here about this same topic (different carriers and different iPhones) and they all have very similar responses to what I've said.  If you search for this topic, you can see all the different questions and answers; I just combined them all.