Fresh from the Vodafone Australia launch this morning, we had a quick look at the new iPhone 3G and its features. Here are our first impressions of the phone and how it compares to the original.

First off: the design. The iPhone 3G has the same screen and basic dimensions as its predecessor, but the older model's squarish shape has been replaced by a much sleeker, tapered look. The new phone is in fact marginally thicker than the original, but it feels smaller and easier to hold. There are two visible screws at the bottom of the iPhone, an odd design choice given Apple's usual perfection in this regard.

[ For the big picture on the iPhone 3G, see InfoWorld's special report, and for more on bringing the iPhone into the office, read How to make the new iPhone work at work. ]

To the praise of all who used their iPhones as portable media players, the iPhone 3G doesn't have a recessed headphone jack. This means that users no longer have to fork out extra cash for iPhone-capable headphones and can use any set that has a standard 3.5mm jack. To the relief of owners of the original iPhone with needle-pierced fingers, Apple packages a SIM eject tool to release the SIM card receptacle.

The iPhone 3G feels slightly slower to use. Everything from waking up from sleep, opening the Springboard, and even the accelerometer registering movement takes a fraction of a second longer than it did with its predecessor. Original iPhone users may notice the difference, but it doesn't really affect the use of the handset. It may be a side effect of the 2.0 Firmware Update rather than the phone's altered hardware.

Users who switch over to the iPhone 3G will immediately notice the difference in the quality of the integrated speakers. The new speakers are much louder and clearer than those on the original iPhone. This makes for bearable speakerphone conversations and a better music-listening experience.

One of the major inclusions in the iPhone 3G is Assisted GPS functionality. Paired with Google Maps, the phone's A-GPS module took under 10 seconds to find our position indoors, a remarkable result rivalling dedicated GPS devices. We weren't able to test Google Maps' ability to give directions for driving or walking. GPS enthusiasts might want to wait a few weeks for TomTom to release its own proprietary software.

As evidenced by its name, the iPhone 3G offers tri-band 3G connectivity for the first time, with the addition of HSDPA capabilities. The effect is immediately noticeable: we compared original iPhone and iPhone 3G side-by-side, with both using Vodafone SIM cards. In the same location, the iPhone 3G picked up full reception; the original iPhone only managed half the possible reception.

Using the Internet is also bearable. The slow EDGE speeds forced many iPhone users to restrict Internet use to Wi-Fi hotspots; the iPhone 3G's HSDPA speeds are fast enough to receive e-mail and conduct some light Web browsing. The speeds still aren't blisteringly fast over Vodafone's 3G network — it took 41 seconds to open the Good Gear Guide site — but it's a major improvement.

The second-generation handset retains some of the original iPhone's flaws. The iPhone's crippled Bluetooth is still evident. The iPhone 3G will pair to a dedicated Bluetooth headset and a PC or Mac, but you can't transfer files, so the phone's Bluetooth is essentially restricted to making and receiving phone calls.

The iPhone 3G is a sleeker, more professional iPhone that benefits from some major refinements. In our full review on Monday, we'll have a more in-depth look at the handset, including MobileMe, the App Store, and Microsoft Exchange and ActiveSync support.