If you followed the keynote, you at least got a small taste of the software based updates coming with the iPhone 3G S. But which ones are exclusive to the 3G S, and which will work on your existing phone?

First, let's have a look at the new software features:

Voice Control (iPhone 3G S)

By simply holding down the Home button, you can give the phone voice commands to dial a contact, dial a phone number, or to control the iPod. You can also get audible feedback about what music is currently playing, and switch to other songs or playlists, without having to switch to the iPod, change music, then switch back to the application you were using previously.

Accessibility (iPhone 3G S)

Though many may think that the accessibility features are only for users with disabilities, there are some other valid uses for them as well. For instance, you could have the phone read text from a web page or an eBook out loud, so that you can focus on other things while listening. VoiceOver might also be handy to announce an incoming text message while you are driving, so that you don't have to take your eyes off the road to know who the message was from. The Zoom and High Contrast features could also be useful to other users who are not 'visually impaired', per se, but who still have difficulty reading text on the smaller screen.

Video Recording / Editing (iPhone 3G S)

Apple decided to pair up a new and better camera with a better Camera application to give users the ability to record, edit and share videos right from their phone. Although this would have worked with the old camera, the additional processing power and memory of the 3G S, coupled with the new camera's enhanced focus features, should make this very simple and easy to use.

MMS (iPhone 3G & 3G S)

Yes, MMS support is finally here, though your carrier must support it, and AT&T doesn't at this time ("later this summer"). You can send videos, pictures, and contact information via MMS, as owners of media-capable phones on other carriers have long known.

Tethering (iPhone 3G & 3G S)

Tethering support is also here, though again your carrier must support it. AT&T's support for tethering, while expected at some point, is unannounced at this time. Many other carriers are supporting it, but in most cases requiring an additional feature to be added to the plan or charging extra for it.

Find My iPhone (All iPhone Models, requires MobileMe subscription)

The Find My iPhone feature of MobileMe allows you to locate your iPhone's position, and optionally send it a message, play an audible alert, or if the phone is indeed lost or stolen, immediately wipe its contents.

Cut, Copy & Paste (All iPhone Models)

The iPhone finally has copy and paste! It sure has been a long time coming, but Apple finally found a good (and simple) way to implement it. You tap and hold on the cursor on a word, and it highlights the current word. You then drag the box around the content you want to copy, then tap copy. Then you just tap on the cursor where you want to insert the content, and choose paste. It also works between all applications on the phone.

Voice Notes (All iPhone Models)

The Voice Notes app is a simple voice recorder that allows you to record short voice notes and save them, or if you have an iPhone 3G/3G S, send them via MMS.

Dock Connector API (All iPhone Models)

The new iPhoneOS 3.0 allows applications to access the dock connector, opening up limitless possibilities to communicating with external devices and equipment.

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You're probably thinking that most of these enhancements should work on the existing 3G iPhone, and you would be right. But keep in mind that the faster processor and increased memory of the S carry some weight. Things like voice recognition and text-to-speech are much more usable when you don't have to wait several seconds for the software to respond.

It is a pretty safe bet that going forward, we will continue to see Apple use additional software features to differentiate the various models of the iPhone, in addition to any hardware differences that may exist.

Besides the software changes outlined above, the iPhone 3G S has a few hardware changes as well:

Processor, Memory and Graphics

Both the original iPhone and the iPhone 3G are powered by an ARM 11 CPU running at about 412MHz, with a 32KB L1 cache. The graphics processor is a PowerVR MBX-Lite GPU, which is a rough equivalent of the NVIDIA Riva TNT2 series of video cards. Both of these are coupled, along with 128MB of DDR memory, on a single chip that is smaller than the Intel Atom line of processors.

By comparison, the iPhone 3G S is powered by the ARM Cortex A8 processor, the PowerVR SGX for graphics (which has a throughput of nearly seven times that of the MBX-Lite used in the previous models), and 256MB of DDR memory. This is the same core configuration that is used in the Palm Pre, for those who are comparing notes. Sure, it may not hold a candle to your desktop gaming rig, but it can definitely hold its own at portable and mobile computing.

Digital Compass

While it may not seem like much at first, the compass will prove to be a very useful device in the new iPhone. Sure, now you'll be able to tell which direction you're facing in Maps, or get turn-by-turn directions, but even better than that will be the ingenious apps that make use of the compass to give you additional controls in games and other applications. By monitoring which direction the phone is pointed, not only can the device tell if it is tilted or twisted, but it can now tell when it is turned or rotated horizontally as well.

3.0 Megapixel Camera

Although most of the improvements to the camera functions of the iPhone are due to ingenious software tricks, some of them still rely on improved hardware behind the scenes to make them tick. In this case, it's an improved 3 megapixel camera sensor, with the ability to take much clearer close-up shots. The software then can use the automatic focus, exposure and macro controls to fine tune the shot.

Nike+ Integration

If you're tired of having to carry both your iPod and iPhone just so that you can use the Nike+, your workout has just become easier. Now the 3G S supports the Nike+ directly, so you can keep track of your run, and use voice commands to switch up the music or make a quick call.

Headphones

One minor detail that has missed time in the spotlight is a minor change to the headphone jack. The 3G S includes Apple's updated earphones that feature an inline remote allowing volume control and voice commands, in addition to the standard mute/play/pause functionality of the previous earphones. The in-ear headphones released a few months ago will also work with the 3G S.

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As you can see, the iPhone 3G S might look just like a regular iPhone 3G, but the extra boosts it gets from an improved processor, better graphics, and increased memory allow it to do quite a bit more, both with built-in applications and 3rd-party apps from the App Store. Add to that the extra capabilities you get with the additional hardware, and you have a pretty formidable package that is capable of just about anything.