The iPhone 3Gs come with lots of free application straight from the box.
For me, the Digital Compass is the most convenient and useful of all. No need to connect to the internet for it to work. You just tap it to open and it’s ready to use.
It will give you your current location base on the readout on the bottom part of the screen. It automatically adjust when you turn and gives you the correct reading every time.
Options are very simple too. Just click the ‘i’ icon on the bottom right side of the screen. It only has two option to choose from the True North and the Magnetic North.
Choosing the True North, will give you accurate reading all the time without interference from any magnetic pull. While the Magnetic North is quite cool, it actually is being affected by any metal or any object that has a magnetic pull.
Here is a video I got giving a complete details of the Digital Compass: