What I don’t mean to include in this new class of devices are netbooks running Microsoft Windows, which are just fine, but are really merely small, cheap laptops. Nor do I mean to include the tens of millions of older, less capable, phones labeled “smartphones,” which can be a slippery term.

These devices, like the Palm Treo, older Windows Mobile phones, or older-model BlackBerries, were breakthrough products in their day. But they use wimpier operating systems and less capable hardware than today’s new class of smartphones. They do run third-party apps, but these look primitive compared with, say, an iPhone app.

A battle is shaping up in the next few years to see who will dominate this new handheld platform–who will attract the most users and third-party apps?

So, here’s a quick snapshot of the strengths and weaknesses of the main combatants in the war for the handheld platform.

Apple

Strengths: Having defined this new class of handheld computers, Apple has a huge head start, with 30 million modern devices running a powerful and attractive operating system. That includes 17 million iPhones, plus Apple’s secret weapon: 13 million iPod Touches, which do almost all that an iPhone does, except connect to the cellphone networks. Apple (AAPL) also has an easy-to-use app store, which is now estimated to hold over 30,000 apps that have been downloaded over 900 million times in just about nine months. The iPhone also offers wireless synchronization via MobileMe and Microsoft Exchange, and has had terrific marketing. And rumors persist that Apple is working on a cheaper iPhone, and/or a larger iPod Touch, in a tablet format.

Weaknesses: Apple has three key vulnerabilities. First, there are millions of people who prefer a physical keyboard, which the iPhone and Touch lack. Second, at least in the U.S., the iPhone is tied to a single carrier, AT&T (T), whose 3G network is still lousy in some major areas. Finally, while the iPhone’s $199 price has been good enough to make it a hit, people in a deep recession might respond better to a lower price, even if it was for a stripped-down lesser model.

Research in Motion

Strengths: The BlackBerry is an icon, beloved by many, with a large installed base estimated at over 50 million. The company has made progress in migrating the BlackBerry to consumers from corporate IT departments. It understands the importance of software, and has launched its own Apple-like app store, with a decent initial selection. It has a robust marketing campaign and is available from multiple carriers. Most models have physical keyboards.

Weaknesses: The new BlackBerry app platform leaves out much of the installed base; it only works on BlackBerry models introduced after the fall of 2006. RIM (RIMM) stumbled with its first touchscreen BlackBerry, the Storm. And its app store, and the apps themselves in many cases, are clumsier and less polished than the iPhone’s. Most of all, the BlackBerry desperately needs a major user-interface overhaul. Email addicts who know lots of shortcuts love the UI, but it’s very dated for a world where the device must do more than email. There are way too many clicks, steps and menus, and the browser is still weak. RIM has just hired a new user interface guru who worked at Apple and Microsoft, so it apparently gets this problem.

Microsoft

Strengths: Windows Mobile has a large installed base, with many developers who created lots of apps for older versions of the software platform. Microsoft (MSFT) also plans an app store. The company has also launched a wireless synchronization service for consumers, called My Phone. Unlike Apple or RIM, Microsoft has a horizontal strategy, which places its platform on the hardware of numerous handset makers and carriers. The operating system can work with or without a physical keyboard.

Weaknesses: Windows Mobile is old. It is less powerful than the iPhone OS or Android, and has a user interface that needs a major redo. The company laughed off the iPhone phenomenon, and is now late in catching up. A minor new release is planned for this year, but Microsoft is racing to do a complete overhaul of Windows Mobile, called version 7. Unfortunately, that won’t be out till 2010. The new app store won’t work with current versions of Windows Mobile.

And, currently, Windows Mobile lacks a killer hardware device. The best Windows Mobile phones today are models from HTC that feature HTC’s own software, which works to hide as much of the hidebound Windows Mobile user interface as possible. It isn’t clear that apps built for the HTC user interface will work properly on regular Windows Mobile phones, and vice versa.

Google

Strengths: Android is modern and powerful–different from, but in the same class with, the iPhone OS. It has an app store, and excellent wireless synchronization with Google’s calendar and contacts. Like Windows Mobile, it’s a horizontal product, which can be used on numerous handsets and even tablets or netbooks, some of which are rumored to be in the works. It will be available on multiple carriers, and can work with or without a physical keyboard.

Weaknesses: The first Android phone, the T-Mobile G1, was clunky and didn’t set the world on fire. The Android app store has so far attracted surprisingly few apps compared to Apple’s at the same stage. Some users might balk at the tight tie-in with Google (GOOG). Handset makers can build Android phones that aren’t tied in to Google services, so it will be important to see how these variants fare. Another problem is that, as versions of Android diverge among handset makers and carriers, app developers may face a compatibility challenge.

Palm

Strengths: With a slug of venture capital money, and the leadership of an ex-Apple exec, Palm has reinvented both its software and hardware, after allowing them to grow stale. The new Palm Pre and its new webOS, which will launch this spring, have impressed those who’ve seen them, and appear to have a real shot at competing with the iPhone and BlackBerry. The new platform is built for wireless synchronization and third-party developers, and, unlike the iPhone, and some planned Android models, the Pre combines its touchscreen features with a  physical keyboard.

Weaknesses: Even if the phone and OS are hailed once reviewers test them, there are many business issues for Palm (PALM). The company is running on fumes, financially, and its launch carrier, Sprint (S), is hemorrhaging as well. That could make it tough to subsidize the Pre enough to compete on price with the iPhone and BlackBerry, especially if Apple does a cheaper iPhone. In addition, Palm will have to mount a costly marketing campaign to match the advertising machines of Apple, RIM and Microsoft. And it may need financial incentives to tempt developers to write apps for the Pre.

Nokia

Strengths: Nokia is the world-wide leader in cellphones, including smartphones (by the loose definition of that term.) It understands that software and cloud services are key, and has launched an online service called Ovi. There are many older apps already for the Symbian operating system that powers most Nokia models, and Nokia (NOK) is working on an app store. The company is good at hardware, and has huge brand loyalty, at least outside the U.S. And its best known smartphones have physical keyboards.

Weaknesses: Nokia’s software has been inferior to Apple’s and Google’s. To fix this, the company has handed off Symbian to an open-source consortium with a complicated structure. That could make Symbian, and thus Nokia, less nimble than Apple, RIM or Google. Some of Nokia’s competitors will also be using this new Symbian, attempting to differentiate their products with user interface and feature differences. Thus as in the case of Android, there’s a danger that, if variations of Symbian diverge too much, application compatibility could become  a problem. The company also has historically been only a minor player in the very important U.S. market.

The phone, expected to be the first of many to use the Android operating system, was largely designed by Google, and was built by HTC of Taiwan. It will be sold in the U.S. starting next month by T-Mobile, for $179 with a two-year contract.

Here are some first impressions of the G1, based on some experience with a prototype. This isn’t a full review; that will come later, when I’ve had a chance to use a more finished device.

Most importantly, the G1 complements its touch screen with a physical keyboard, the lack of which has made the iPhone a non-starter for some users. The G1’s keyboard is revealed when you slide open its screen. The keys are a bit flat, and you have to reach your right thumb around a bulging portion of the phone’s body to type, but it’s a real keyboard. And there’s also a BlackBerry-like trackball that supplements the touch screen navigation. I found typing on this keyboard to be OK, but not great.

A second big feature, or limitation, of the G1 — depending on your point of view — is that it is tightly tied to Google’s web-based email, contacts and calendar programs. In fact, you must have a Google (GOOG) account to use the phone, and can only synchronize the phone’s calendar and address book with Google online services. Unlike the iPhone, it doesn’t work with Microsoft Exchange, and it can’t physically be synced with a PC-based calendar or contacts program, like Microsoft Outlook.

So, if your world already revolves around Google services, you may find that the G1 fits like a glove. If not, you may be disappointed.

Also, like the iPhone, the G1 has a download service for third-party programs, called Market. I downloaded a couple of simple Market programs and they worked fine.

The G1 won’t win any beauty contests with its Apple (AAPL) rival. It’s stubby and chunky, nearly 30% thicker and almost 20% heavier than the iPhone. It’s a bit narrower — more like a standard phone than a “smart phone” — and longer, but has a somewhat smaller screen.

Still, it feels pretty good in the hand when closed, although I found it more awkward when opened.

But the software is slick. Programs appear in a virtual drawer you slide open via a tab at the bottom of the screen, and notifications of new messages and the like can be read by sliding the top bar of the screen down. The screen and software were quick and responsive.

The web browser is based on the same open-source technology as the iPhone’s, but works differently. You can view a portion of a page, and use a zoom control and finger-dragging to see the rest, or you can view the whole page in miniature, as on the iPhone. In the latter mode, however, you can’t simply use Apple’s technique of tapping or “pinching” to zoom in on a portion of a page. You must move around a virtual lens to pick out a part of the page on which to focus.

There are two email programs: one for Google’s Gmail, another for all other email services. There’s an instant messaging program, that works with multiple services — not just Google’s. And, as on the iPhone, there are programs for using Google Maps and Google’s YouTube video service. The G1’s Google Maps program has a feature lacking in the iPhone version: photographic street views of some locations.

The G1 has a couple of other things the iPhone omits: copy and paste functionality and a so-called MMS program, which sends photos to other phones without using email. Its camera is higher-resolution than the iPhone’s, but, like Apple’s, doesn’t record video.

It also gives you far more flexibility in organizing your desktop, or home screen, than the iPhone, or almost any phone I’ve seen. In addition to placing icons for programs there, you can place everything from individual contacts, music playlists, folders, web pages, and more.

The G1’s multimedia capabilities are less polished and complete than the iPhone’s. There’s a very basic music player, and a built-in version of Amazon’s MP3 download service that works fine. But the G1 lacks a built-in video player — you have to download one from the third-party software store. Also, you cannot use standard stereo headphones with the G1. You need special ones, or an adapter.

And it lacks the iPhone’s ability to change the orientation of a web page or photo by just turning the phone. You also can’t move through groups of photos by just “flicking,” as on the iPhone.

The G1 also has much less memory than the iPhone. The base $199 iPhone comes with 8 gigabytes sealed in, but the G1 comes with just a 1 gigabyte memory card. Its maximum memory, if you buy a bigger card, is 8 gigabytes, while the iPhone can be purchased (for $299) with twice that.

T-Mobile is claiming similar talk time to that of the iPhone, but, unlike Apple’s product, the G1 has a removable battery.

Finally, a word about networks. In the U.S., the G1 will initially only be available on T-Mobile, whose high-speed 3G network will be up and running in many fewer cities than those of its larger rivals, AT&T (T) and Verizon (VZ). Like the iPhone, the G1 does have Wi-Fi, Bluetooth and GPS.

In sum, the G1 is a powerful, versatile device which will offer users a real alternative in the new handheld computing category the iPhone has occupied alone.