Here’s how to make your iPhone display a location that’s different from the one you’re really at:
Note that whenever you need to change the coordinates, you will need to have the iPhone connected to your computer. Once you disconnect the phone it will retain the last location set. To reset the phone to your real location, just restart it.
If you don’t want to get your hands dirty, you can also use this piece of software: iTools.
If you want to obtain the GPS coordinates for any location on earth, use this site.