If you’re building applications for mobile devices, are you an indy, a corporate or an enterprise IT developer? The world is trifurcating into those specific communities.

I spent most of last week at Microsoft MIX, the company’s annual technical conference for Web developers. This year, the event had a huge concentration on both Silverlight and Windows Phone 7. There’s a connection between the two, of course: Windows Phone 7 appears to be mainly a delivery platform for Silverlight applications.

Looking forward, I see the three hot mobile app platforms are going to be Apple’s iPhone and iPad (which share the same SDK and programming model), Google’s Android, and Windows Phone 7.

The iPhone has a huge first-mover advantage because of its incredible head start. Even so, developers chafe under Apple’s tight control over the distribution channel (the iTunes Store).

Android is still ramping up, but version 2.1 of the SDK has captured a lot of attention from open-source developers.

Windows Phone 7 won’t ship for many months and breaks the app model used with Windows Mobile 6.5. Still, because it uses familiar tools like Visual Studio, I predict that it’ll become popular with Microsoft developers.

That brings us to the indy, corporate and enterprise IT question.

The iPhone/iPad business model is focused on supporting two main groups of developers (which I’ll call corporate and indy), but not enterprise IT developers.

Corporate: Large companies are writing apps that tie into their mainline businesses, such as the news reader from The New York Times, the Facebook mobile app, Amazon’s Kindle reader, and so on. Those corporate developers see the apps as a way to serve their customer base: as an adjunct, perhaps, to their websites.

Indy: To independent developers, the mobile app is the primary product used to make money. Often there’s a “lite,” free version, which is meant to entice the customer to buy a paid version. But for those developers, it’s all about selling the apps.

Enterprise IT: Apple’s iTunes distribution model is designed for selling or giving away software to consumers. It’s not appropriate for a company to build applications to be used by its employees only. If enterprise developers want to support employees with the iPhone or iPad, they should use a tuned website, not a native app. That makes the iPhone/iPad less than ideal as an IT platform.

The Android platform is compelling to indies and enterprise IT developers because there’s no Apple-style restriction on app distribution. It’s great for building custom software for employees and partners. It’s also very appealing to indy developers who want to build apps that Apple doesn’t want to stock in its store for either quality or content reasons. Plus, it’s fine for corporate developers to create Android apps that support their other business interests.

The biggest weakness is the lack of a central marketing machine (like the Apple iTunes Store) to drive revenue for indies. So while we’ll see lots of Android apps, we’re unlikely to see as much developer revenue.

Windows Phone 7 will be more like Android than the iPhone. It should prove especially popular with enterprise IT departments because they will find it easiest to build, deploy and manage apps on Windows Phone 7 devices. Plus, Microsoft is unparalleled in supporting enterprise IT developers with tools, training and third-party ecosystem partners.

If the phone sells well, it will also be attractive to corporate developers. For indies, much depends on how strong Microsoft’s marketing programs are; beyond the Xbox, Microsoft has little track record there, and its attempts to build a business around the Zune have been disappointing.

So tell me: Are you an indy, a corporate or an enterprise IT developer? What’s your take on the iPhone/iPad, Android and Windows Phone 7? Write me at feedback@bzmedia.com.

Alan Zeichick is editorial director of SD Times. Follow him on Twitter at twitter.com/zeichick. Read his blog at ztrek.blogspot.com.