I think the new Apple iPhone 3G is a terrific device, and you have to admire Apple's design and user-interface prowess. We want to be wowed by technology, and Apple does it.
However, there are three "buyer beware" tips to keep in mind before you get in line for an iPhone 3G on July 11. I've been researching the iPhone 3G extensively because this new model includes GPS.
1. It's not a substitute for an in-car portable GPS navigator (at least not yet, and maybe not for a long time to come). When you activate the iPhone 3G's maps application and the GPS tracking mode (GPS tracking mode is not on all of the time to conserve battery life) the iPhone 3G locates you on a Google map, and keeps your position centered on the map as you move. You can then do a search for points of interest, such as restaurants, or ask for directions. When you ask for directions, you will be shown a highlighted route on the map, and turn-by-turn text directions. It's essentially the Google Maps "get directions" feature with real-time location display. However, it does not offer the real-time 3D views, anticipatory text-to-speech directions, estimated arrival time, and many other features that make good quality in-car portable GPS navigators effective and safe in traffic. And there may be a bottleneck for new applications that could do better for the driver, because Apple's software development license places restrictions on "real-time route guidance" applications.
2. You may not get the "two times faster" 3G speed you are paying for. In all of the run-up promotion and publicity for the iPhone 3G, it's not mentioned that iPhone 3G's exclusive carrier, AT&T, does not cover much of the country with 3G speed service. Yes, most of the major metro areas are covered, but do yourself a favor and consult this AT&T 3G coverage map before you buy.
3. You will pay more per month, and if you are already an AT&T customer, you may not be "eligible" to upgrade to the iPhone 3G right away. The mobile phone and iPod guides at About.com have done an excellent job of summing up the costs and restrictions.