Here are our first impressions of Apple's new iPhone 3G, based on preliminary tests in our lab. Overall, the 3G is an improvement on its predecessor, though, as we found, there's still a lot of room left for improvement.  The details:

3G performance is fast. The new iPhone can use AT&T's faster 3G network, where available; the original iPhone could only trudge along on AT&T's creaky 2G EDGE network. In our tests, the new iPhone was about twice as fast when using the 3G network than the 2G. It took just 30 seconds to download the front page of the New York Times in our lab, compared with a minute to download the same page over the EDGE network. In fact, surfing the Web on the iPhone was even faster than on another high-profile phone that uses 3G: Verizon's LG Voyager. The phone allows you to select the EDGE network to conserve battery life. According to Apple, talk time in EDGE mode should be about 10 hours, compared with about 5 hours when iPhone is in 3G mode. We'll check both those claims early next week.

Better GPS navigation. Our Cars colleagues have completed an initial, real-world session. While the team has only just begun its full, authoritative test, their initial impression is that the iPhone 3G does indeed improve over the previous iPhone in pinpointing your location. However, the navigation ability does not approach that of previously tested competing GPS-enabled cell phones nor dedicated navigation devices.

Still a great screen. The new iPhone's screen appears to be comparable to the old one. That is, readability of text was still excellent thanks to the large, high-resolution display, which had no trouble handling different font sizes, colors, and formats such as bold, italic, and underline.

Office documents: Look, but don't edit. We were able to view attachments such as MS Word and Excel files. But the 3G, like its predecessor, doesn't allow you to edit or create new documents, as you can with phones that run on Windows Mobile or Palm operating systems. We were also able to view PowerPoint files—a nice touch that the old iPhone lacked—though we couldn't view them as individual slides. Rather, those slides appear as a list that you have to scroll through. The iPhone can't open ZIP attachments, which many BlackBerry, Palm, and Windows Mobile smart phones can do. You also can't use the 3G as a mass storage device to shuttle files back and forth between home and the office, as you can with many smart phones and even Apple's own iPods.

Our initial take: What was, hands-down, the best multimedia smart phone on the market just got a heck of a lot better. But as a corporate instrument, the 3G may still need a little more polish.

—Mike Gikas