The second major addition is built-in GPS. Although the original iPhone can approximate your location by triangulating between available mobile phone towers and known Wi-Fi hot spots, its effectiveness varies widely depending on where you are; It could be within 10 or 20 feet in one spot and off by a mile or two off just a short drive away. The iPhone 3G's GPS could pinpoint my location to within less than five feet in almost any location I tried. And despite some concerns from veteran GPS users that the iPhone might take a long time to acquire GPS signals and calculate a position, I found it could do so within a minute on each try.

That said, some structures (like the 150-year-old brick brownstone in which I live) can impede the reliable acquisition of GPS signals. If that happens, the iPhone 3G will fall back on the triangulation method. To clue you in on which method is being used, the images displayed in the Maps application will vary. Real GPS locations are displayed as a 3-D blue dot; locations based on the less precise method are shown with the same two dimensional blue circle used on older iPhones.

GPS is also fully real-time, so you can watch on a map or satellite image (or a hybrid view) view as you move (either on foot or by car) from place to place. The feature also integrates well with using Google Maps for directions. I should note that the Maps application also integrates well with other address-sensitive features on the iPhone (either model) such as contact addresses or the search feature. While turn-by-turn navigation isn't yet available on the iPhone 3G, the combination of GPS and Maps are a fully useable alternative. Move over Garmin.

I also can't help pointing out the cool factor -- or, depending on your point of view, the scary, big-brother factor -- of using the GPS capabilities with a satellite view or hybrid map view. With the availability of discernible images of objects as small as cars and trash cans, just walking around the neighborhood -- while looking at the Maps application and watching it zoom and re-center as I entered addresses or requested my current location -- offered a distinct spy/sci-fi movie feeling. I'm just not sure if it's closer to James Bond or Minority Report.

One of the real advantages of built-in GPS is that any iPhone developer can now use the iPhone 3G's location services. Several free applications already available through the App Store already use this feature, including the LoopT social networking app and Near Pics, which displays photos of landmarks near wherever you happen to be. As more developers find innovative ways to offer location-based services, the GPS advantages will only grow.

Bring on the apps

Of course, not all new features are specific to the iPhone 3G. The iPhone 2.0 firmware update also released Friday adds a variety of features to first-generation iPhones. The biggest is support for third-party applications via the App Store, which exists as both a standalone application on the iPhone itself and as a segment of the iTunes Store, allowing users to browse, purchase, and download applications from the device itself or using their computers.

With more than 550 applications across a wide range of genres already available -- we're talking about everything from games to foreign language phrasebooks to dedicated social networking tools -- the App Store is a boon for any iPhone user. With about a quarter of the applications available for free, there's no reason for any iPhone owner to not be excited. Even the paid applications are inexpensive and generally sell for US$9.99 or less.