(on a Mac)
Open your iPhone photo, or any geotagged photo, in Preview. It's normally the default viewer already.
Open the Inspector window for a photo, Command-I or Tools Menu->Inspector.
Select the middle group at the top, (comic bubble with an "!").
You will see tabs to display all the metadata inserted by the camera.
If there is geo-data, you will see a GPS tab. If none, the tab will not be present.
Select the GPS tab to see the coordinates and a mini-world map with crosshairs at the location.
Click the locate button in the panel to open Google Maps to the photo location! Cool, huh?
Doug Korns