Without fail, the moment Apple launches a great product or new revision, within moments talk quickly shifts back to "what's next?!" Last month it was the iPod and iTunes. This month it's the MacBook. But with Macworld slowly ramping up, and competitors slowly turning iClones into specced out SuperClones, the blogsphere spotlight will inevitably turn back to the iPhone, and just what device they'll dent our universe with next.

What if it's an iPhone HD?

The Next Big Thing. The Paradigm Shift. The Mobile Computing Platform. All of these monickers have been applied to the iPhone, it's multi-touch interface and it's mobile OS X implementation. Rightly so. While other companies have fragmented their mobile strategies among many different form factors, from different manufacturers, some even running different versions of the OS itself, Apple has remained remarkably consistent and ingeniously integrated.

The result? What worked on the original iPhone 2G and iPod Touch also works flawlessly on the second generation iPhone 3G and iPod Touch. Four devices spanning tens of millions of users, all with unprecedented unity and utility.

Apple accomplished this via 2008 revisions that were relatively minor in terms of the platform, yet simultaneously crucial in terms of the feature set. The iPhone really needed 3G and GPS to be competitive internationally, and to a lesser extent the iPod Touch really needed external volume and speakers to cross over into serious entertainment and gaming.

This gave consumers an utterly painless upgrade path, and removed from developers the burden of having to worry about whether any specific device might have a touchscreen or not, a keyboard or not, a trackball or not, etc. If you have an iPhone 2G as opposed to 3G, your internet experience is the same, just slower. If you don't have GPS, your location services are the same, just less precise. This is one of the less discussed but most important advantages of the current iPhone roadmap.

But what's next? What similar revision can Apple do in 2009 to further expand the iPhone platform without breaking compatibility at the same time?

Simple. HD. High Definition video.

The current iPhone and iPod Touch line features what was a very impressive 480x320 screen, and Apple has shown they can deliver that screen at a whopping 202dpi on the last generation iPod Nano.

back at Macworld 2008 (one year after introducing the original iPhone 2G), Apple announced HD movie rentals for the Apple TV and this September, they announced HD TV Shows. The world is moving inexorably towards HD and Apple and iTunes are pretty much keeping pace with it. Not only that, they're laying the pipes. Gizmodo even revealed that the exiting iPhone can already handle HD signals "just fine".

Competitively speaking, RIM is launching a slightly higher resolution screen on their Blackberry Storm, at 480x360, and at the small sizes of handset displays, every pixel matters.

Meanwhile, the HTC Touch HD is flaunting a massive 800x480p screen, and though it may not be hitting North American shores any time soon, HTC is clearly readying even more high density handsets, likely for both Windows Mobile and Google's Android.

Of course, these devices are plagued with either outdated OS or fragmented hardware, which will be limiting factors going forward, but they serve to send Apple a powerful message as to where the technology is going, and what Apple can do to continue leading the way.

Announced with pre-requisite BOOM! by Steve Jobs on stage at Macworld 2009 -- or WWDC in June -- with an 800x480p display at 202dpi-like density would move the platform forward an could do so in the same, unified way as the iPhone 3G.

Resolution independence in the iPhone SDK -- the same type talked about for years in Mac OS X -- and simple things like using vector/PDF icons, buttons, and other GUI elements, rather than non-scalable bitmaps could keep development focused and users from worrying which device what App might work on. If you have an iPhone 3G (or 2G) your visual experience is the same, just lower resolution than the HD. (i.e. the same icon takes up the same physical space on your Home screen, just isn't rendered with as many physical pixels on the screen).

The only problem? HD is BIG. It takes up space. Even with H.264 compression, the size quickly adds up and the storage space rapidly disappears. The solution to this is one many people expect to see anyway: 32GB. The iPod Touch already has this option by virtue of having twice the NAND chip slots as the iPhone (since the iPod Touch doesn't need to save space for cellular or Blue Tooth radios). Double capacity NAND chips exist, however, and Apple will switch to them as soon as pricing and availability make it reasonable to do so. (Yes, that would also mean a 64GB iPod Touch -- more capacity than the original Apple TV shipped with!)

Add to this a better spatial speaker system and some form of virtualized surround sound out, combined with 720p video out through the already existing component cables available from Apple, and you have a compelling, and amazingly portable, HD offering as well. Scratch that. Add 802.11n WiFi and streaming to and from iTunes and the Apple TV, and you have a KILLER HD offering. (One that wouldn't even be bound by on-device storage any more.)

Along with the necessary 3.0 firmware update to enable all this HD goodness, 2009 could be another spectacular -- if evolutionary -- year for the iPhone.

It makes sense technological, and it's becoming increasingly important competitively. Just802.11n streaming, 32GB iPhone HD, running firmware 3.0, in 2009.